OKLCH in CSS: why we moved from RGB and HSL

Cover for OKLCH in CSS: why we moved from RGB and HSL

Topics

Share this post on


Translations

If you’re interested in translating or adapting this post, please contact us first.

In CSS, we’ve been encoding colors with rgb() or hex (mostly for historical reasons). However, the new CSS Color 4 specification adds many better ways of declaring colors in CSS. Of these, oklch() is the most interesting one—this article explains why.

The extremely short version

oklch() is a new way to define CSS colors. In oklch(L C H) or oklch(L C H / a) each item corresponds as follows:

  • L is perceived lightness (0%-100%). “Perceived” means that it has predicted contrast, unlike L in hsl().
  • C is chroma, from gray to the most saturated color.
  • H is the hue angle (0-360).
  • a is opacity (0-1 or 0-100%).
a:hover {
  background:   oklch(45% 0.26 264); /* blue */
  color:        oklch(100% 0 0);     /* white */
  color:        oklch(0% 0 0 / 50%); /* black with 50% opacity */
}

The benefits of OKLCH:

  1. Unlike rgb() or hex (#ca0000), OKLCH is human readable. You can easily understand what color an OKLCH value represents simply by looking at the numbers. It works like HSL, but OKLCH encodes lightness better than HSL.
  2. Unlike hsl(), OKLCH is better for color modifications. It uses perceptual lightness and has predictable contrast. No more unexpected results, like we had with darken() in Sass.
  3. Further, with its predictable contrast, OKLCH has better a11y. Especially for pallet generation in design systems.
  4. OKLCH can be used for wide-gamut P3 colors. For instance, new devices (like those from Apple) can display more colors than old sRGB monitors, and we can use OKLCH to specify these new colors.

But, that being said, alongside OKLCH comes two challenges:

  1. With OKLCH and LCH, not all combinations of L, C, and H will result in colors that are supported by every monitor. Although browsers will try to find the closest supported color, it’s still safer to check colors using our color picker.
  2. OKLCH is a new color space. At least for now, at the time of this writing in 2022, its ecosystem is still limited. But we already have oklch() polyfill, palette generator, color picker, and many converters.
The OKLCH color picker by Evil Martians shows the OKLCH space and lightness, chroma, alpha, and hue sliders.

OKLCH space in color picker

So, that’s the short version, but if you want the whole story, let’s start from the beginning in the next section.

Table of contents:

  1. How CSS colors have changed
  2. Comparing OKLCH with other CSS color formats
  3. How OKLCH works
  4. How to add OKLCH to your project
  5. Summing up the results

How CSS colors have changed

CSS Colors Module 4

A little recent history: the CSS Color Module Level 4 specification become a candidate recommendation on July 5, 2022.

It added new syntactic sugar to color functions, which we will use in this article:

.old {
  color:   rgb(51, 170, 51);
  color:   rgba(51, 170, 51, 0.5);
}
.new {
  color:   rgb(51 170 51);
  color:   rgb(51 170 51 / 50%);
}

But more importantly, CSS Color 4 also added 14 new ways to define colors—and these are not just syntactic sugar. These new color-writing methods (like oklch()) improve code readability, a11y, and have the potential to add new features to your website.

P3 Colors

Modern displays can’t actually show all the colors which are really visible to the human eye (the current standard of colors subset is called sRGB). New screens fix this a bit, since they add 30% more new colors; this new set of colors is called P3 (also known as wide-gamut). In terms of adoption, all modern Apple devices and many OLED screens have P3 color support. So, this isn’t something from the distant future—this is happening now.

This additional 30% of color can be very useful for designers:

  • Some of these new colors are more saturated. Thus, you can produce more eye-catching landing pages.
  • The additional colors give your designers more flexibility with palette generation for their design systems.
On the left, a shape shows the extra colors P3 colors gives us from sRGB, represented as an extended wedge from the original shape. On the right, an icon is rendered on the left in sRGB, and a more vibrant icon is rendered on the right with P3 colors, showing how they are more vibrant.

Newly available P3 colors for green on the left. Real-world icon comparison with sRGB vs. P3 on the right.

So, we have P3 colors! That’s great and all, but to actually use them, we’ll need to find a color format in order to support P3. rgb(), hsl(), or hex formats can’t be used to specify P3 colors. We could, however, use the new color(display-p3 1 0 0), but it still shares the readability problems of the RGB format.

Luckily, OKLCH has a good readability, supports P3 and beyond, as well as any color visible to the human eye.

CSS Native Color Manipulations

While it’s true that CSS Color 4 is a big step forward, the upcoming CSS Color 5 will be even more useful; it will finally give us native color manipulation in CSS.

/* These examples use hsl() for illustration.
   Don't use it in real code since hsl() format has bad a11y. */
:root {
  --accent:   hsl(63 61% 40%);
}
.error {
  /* Red version of accent color */
  background:   hsl(from var(--accent) 20 s l);
}
.button:hover {
  /* 10% lighter version */
  background:   hsl(from var(--accent) h s calc(l + 10%))
}

With this new syntax, you can take one color (for instance, from a custom property) and change the individual components of the color format.

Still, as mentioned, there is a drawback to this approach since using the hsl() format is bad for a11y. Results will have unpredictable contrast because the l values are different for different hues.

A familiar refrain emerges: we need a color space where color manipulations produce expected results. Like, for instance, OKLCH.

:root {
  --accent:   oklch(70% 0.14 113);
}
.error {
  /* Red version of accent color */
  background:   oklch(from var(--accent) l c 15)
}
.button:hover {
  /* 10% lighter version */
  background:   oklch(from var(--accent) calc(l + 10%) c h)
}

Note: You don’t need to use OKLCH to input the --accent colors of oklch(from …), but using a consistent format is better for code readability.

Comparing OKLCH with other CSS color formats

Hopefully the previous section gave you some context about where we’ve been, where we are, and where we’re going, as well as oklch(), P3 colors, native color manipulation, and how they all fit together. Of course, rather than just going all in with OKLCH, we could mix and match formats, using different color formats for things like custom properties, P3, or color modifications as needed—but, naturally, having the same color format for most tasks is much better for code maintainability.

So, with this in mind, let’s go ahead and assume that we’ll try to find just one color format for the future of CSS. I believe that format should meet the following criteria:

  1. It should have native CSS support.
  2. The format must be able to encode wide-gamut color: P3 and beyond.
  3. It should be well suited to color modification:
    • This includes a human-readable axis (lightness instead of amount of red).
    • All axes should be independent. Changing the value of a hue’s axis color should maintain the same level of contrast. Saturation changes should not change hue.

So, now that we have our criteria in mind, let’s compare formats.

OKLCH vs. RGB/Hex

The color formats rgb(109 162 218), #6ea3db, or the P3-analog color(display-p3 0.48 0.63 0.84), each contain 3 numbers that represent the amount of red, green and blue. Note: 1 in color(display-p3) encodes a larger value than 255 in RGB.

The above formats all share essentially the same problem: they’re completely unreadable for most developers. Instead, people just use them like they are some sort of magic number, absent of any real understanding or way to compare them.

RGB, hex and color(display-p3) aren’t convenient for color modifications because, for the vast majority of humans, it’s difficult to intuitively set colors by changing the amount of red, blue and green. Further, RGB and hex also can’t encode P3 colors.

On the other hand, OKLCH, LCH, HSL have values we can set that are much closer to the way people naturally think about colors. OKLCH and LCH contain 3 numbers which, respectively, represent the following: lightness, chroma (or saturation), and hue.

Compare hex and OKLCH:

.button {
  /* Blue */
  background:   #6ea3db;
}
.button:hover {
  /* More bright blue */
  background:   #7db3eb;
}
.button.is-delete {
  /* Red with the same saturation */
  background:   #d68585;
}
.button {
  /* Blue */
  background:   oklch(70% 0.1 250);
}
.button:hover {
  /* A brighter blue */
  background:   oklch(75% 0.1 250);
}
.button.is-delete {
  /* Red with the same saturation */
  background:   oklch(70% 0.1 20);
}

OKLCH’s intuitive values sound great, no? But, here’s where we need to talk about the flip side of the coin—the main disadvantage of OKLCH: unlike the others, it has a “young” color space and the ecosystem is still in the development process.

OKLCH vs. HSL

Now, let’s move on and compare OKLCH with HSL. HSL contains 3 numbers to encode hue, saturation, and lightness, like so: hsl(210 60% 64%). The main problem with HSL is that it has a cylindrical color space. Every hue has the same amount of saturation (0—100%). But in reality, our displays and eyes have different max saturations for different hues. HSL hides this complexity by deforming the color space and extending colors to have the same max values.

4 illustrations. The top row shows HSL and OKLCH color spaces with the same chroma/saturation values. On the bottom, the same, but in black and white.

Hue-Lightness slice of HSL and OKLCH spaces with the same chroma/saturation and black-and-white versions below. HSL lightness is not consistent across hue axes.

As a result, an HSL-deformed color space can’t be used for proper color modifications; here, the L (lightness) component is not accurate. Different hues represent different “real” lightness values. This leads to issues with contrast and bad accessibility.

Here are a few real use case examples to demonstrate this problem:

  1. Adding 10% lightness will have different results for blue and purple colors. SASS users may remember how darken() generates unexpected results.
  2. Hue changes (for instance, producing an error-like red color using a company’s accent color) could also change lightness, thus making text unreadable.
There are 4 buttons. The first column is HSL, the second is OKLCH. The bottom-left button has poor contrast due to hue change in HSL.

In HSL, hue changes could lead to accessibility issues from low contrast

HSL is bad for color modification. Many teams have asked the community to avoid HSL for design system palette generation. Additionally, like RGB and hex, HSL can’t be used to define P3 colors.

OKLCH doesn’t deform the space; it shows the real color space with all its complexity. On one hand, this feature allows us to have predictable contrast values after color transformations and P3 color definition. But, on other hand, not all number combinations in OKLCH generate visible colors: some are only visible on P3 monitors. But there’s still some good here: browsers will render the closest supported color.

OKLCH vs. Oklab & LCH vs. Lab

CSS has two functions for Oklab space: oklab() and oklch() and the same for Lab: lab() and lch(). So, what’s the difference?

While they use the same space, they use different ways of encoding a point in this space. Oklab and Lab cartesian coordinates (a: the green/red value of a color, b: blue/yellow value), and OKLCH and LCH use polar coordinates (angle for hue and distance for chroma).

There are two circles to illustrate the difference between Oklab's cartesian coordinates, with a right angle showing a and b, and OKLCH's polar coordinates, which appear as an acute angle with the top ray labeled as 'chroma' and the angle itself labeled as 'hue'.

Cartesian coordinates (Oklab) vs. polar coordinates (OKLCH) in Oklab space

In short, OKLCH and LCH are both better choices for developer readability and color modification because the chroma and hue values are closer to how people actually think about color, rather than simply a and b.

OKLCH vs. LCH

LCH is a good format on top of the CIE LAB (Lab) space that was created to solve all the problems of HSL and RGB. It can encode P3 colors and, in most cases, produces predictable color modification results.

But LCH has one painful bug: an unexpected hue shift on chroma and lightness changes in blue colors (between hue values of 270 and 330).

Two triangles that are constant-hue slice of LCH and OKLCH spaces with the same hue. The LCH slice, the leftmost triangular shape, is blue on one side and purple on the other. The right shape, OKLCH, keeps a constant hue, as expected.

A constant-hue slice of LCH and OKLCH spaces with the same hue. The LCH slice is blue on one side and purple on the other. OKLCH keeps a constant hue as expected.

Here is a small real case:

.temperature.is-very-very-cold {
  background:   lch(35% 110 300);
  /* Looks blue */
}
.temperature.is-very-cold {
  background:   lch(35% 75 300);
  /* We changed only lightness,
     but blue became purple */
}
.temperature.is-cold {
  background:   lch(35% 40 300);
  /* Very purple */
}
.temperature.is-very-very-cold {
  background:   oklch(48% 0.27 274);
  /* Looks blue */
}
.temperature.is-very-cold {
  background:   oklch(48% 0.185 274);
  /* Still blue */

}
.temperature.is-cold {
  background:   oklch(48% 0.1 274);
  /* Still blue */
}

The Oklab and OKLCH spaces were created to solve the hue shift bug.

But OKLCH isn’t merely a bugfix. It also has nice new features related to the math behind color axes. For instance, it has improved gamut correction and CSSWG recommends using OKLCH for gamut mapping.

How OKLCH works

A little bit of history

The Oklab & OKLCH color spaces were created by Björn Ottosson in 2020. The primary reason they were created was to fix the CIE LAB & LCH issue. Björn wrote a great article detailing the reasons he made them and their implementation details.

To be clear, Oklab is very young and this is its primary weak point.

But, after just 2 years, Oklab has already seen very good adoption:

I personally think, that the big changes coming with CSS Colors 4 and 5 are a good time to grab the latest and best solution. In any case, we’ll need to create a new ecosystem around new features from new CSS specs.

Axes

Colors in OKLCH are encoded with 4 numbers. In CSS, it looks like this: oklch(L C H) or oklch(L C H / a).

Four bars show the OKLCH axes. The top-left is lightness; it begins with a dark purple, becoming a light purple as it moves to the right, and eventually there is a hard change to white. The top-right bar is chroma; it begins as a grayish purple and transitions to a light purple, from roughly 33% of the bar to the right there is a hard change to white. The bottom-left is alpha: an alpha channel transitions to a light purple as it stretches to the right. The light purple reaches the end of the bar's left side. The bottom-right is hue: a range of vibrant colors transition as the bar goes from left to right.

OKLCH axes

Here’s a more detailed explanation of each value:

  • L is perceived lightness. It ranges from 0% (black) to 100% (white). The % is mandatory even for zero values.
  • C is chroma, the saturation of color. It goes from 0 (gray) to infinity. In practice there is actually a limit, but it depends on a screen’s color gamut (P3 colors will have bigger values than sRGB) and each hue has a different maximum chroma. For both P3 and sRGB the value will be always below 0.37.
  • H is the hue angle. It goes from 0 to 360, through red 0, yellow 70, green 120, blue 200, purple 300 and then back to red. Since it is an angle, 0 and 360 encode the same hue. H can be written with units 60deg, or without 60.
  • a is opacity (0-1 or 0-100%).

Axes have a different size. 1% for lightness is just 1%, for chroma it is 0.004, and for hue it is 3.6.

Here is a few examples of OKLCH colors:

.bw {
  color:   oklch(0% 0 0);       /* black */
  color:   oklch(100% 0 0);     /* white */
  color:   oklch(100% 0.2 100); /* also white, any hue with 100% L is white */
  color:   oklch(50% 0 0);      /* gray */
}
.colors {
  color:   oklch(80% 0.12 100); /* yellow */
  color:   oklch(60% 0.12 100); /* much darker yellow */
  color:   oklch(80% 0.05 100); /* quite grayish yellow */
  color:   oklch(80% 0.12 225); /* blue, with the same perceived lightness */
}
.opacity {
  color:   oklch(80% 0.12 100 / 50%); /* transparent yellow */
}

Note, that some components could have none as a value. This may occur after a color transformation. For instance, white has no hue, and browsers will parse none as 0.

.white {
  color:   oklch(100% 0 none); /* valid syntax */
}

Color modifications

In CSS Colors 5, we’ll be able to have native color modifications. This will shine a light on one of my favorite perks of OKLCH: it’s the best color space for color modification because it has very predictable results.

Color modification syntax looks like this:

:root {
  --origin:   #ff000;
}
.foo {
  color:   oklch(from var(--origin) l c h);
}

The origin color (var(--origin) in the example above) can be:

  • A color in any format: #ff0000, rgb(255, 0, 0), or oklch(62.8% 0.25 30).
  • A CSS custom property with a color in any format.

Each component (l, c, h) after from X can be:

  • A letter (l, c, h), which indicates to keep the component the same as it was in the origin color.
  • A calc() expression. You can use a letter (l, c, h) instead of a number to reference the value in the origin color.
  • A new value, which will replace the component.

It may sound complex, but some seeing some examples can help illustrate:

:root {
  --error:   oklch(60% 0.16 30);
}
.message.is-error {
  /* The same color but with different opacity */
  background:   oklch(from var(--error) l c h / 60%);
  /* 10% darker */
  border-color:   oklch(from var(--error) calc(l - 10%) c h)
}
.message.is-success {
  /* Another hue (green) with the same lightness and saturation */
  background:   oklch(from var(--error) l c 140);
}

The predicted contrast of OKLCH is very useful when generating accent colors from user input (check an example with our OKLCH color picker):

:root {
  /* Replace lightness and saturation to a certain contrast */
  --accent: oklch(from (--user-input) 87% 0.06h);
}

body {
  background: var(--accent);
  /* We do not need to detect text color with color-contrast()
     because OKLCH has predicted contrast.
     All backgrounds with L≥87% have good contrast with black text. */
  color: black;
}

Gamut correction

OKLCH has an another interesting feature: device independence; OKLCH wasn’t just created for current monitors with sRGB colors.

You can encode any possible color with OKLCH: sRGB, P3, Rec2020 and beyond. Some number combinations will require a P3 monitor to be displayed. For some other combinations, the proper monitors necessary for their display have still yet to be created.

But really, don’t worry about being out of the gamut (the colors supported by a user’s monitor); browsers will render the closest possible color. Finding the closest color in another gamut is called “gamut mapping” or “gamut correction”.

This is why you can see holes in axes of the OKLCH color picker: every hue has a different maximum chroma. Unfortunately, this isn’t just a problem with OKLCH color encoding, it is a limit both of currently available monitors, and our vision. For some lightness values, there is only a blue color with a large chroma. For other lightness values, a green color will not have a corresponding pair in a blue or a red with the same chroma.

A graph with two axes, C on the left and H on the bottom, shows a shape that has huge circular bites missing; as the shape moves from left to right, various colors are seen, appearing as multiple transitioning gradients.

For 44% lightness only blue has high chrome colors visible on sRGB screens

There are 2 ways of gamut mapping:

  • Convert the color to RGB (or P3) and clip values above 100% or below 0%: rgb(150% -20% 30%)rgb(100% 0 30%). This is the fastest method, but it has the worst results—it could change a color’s hue and this change will be visible to users.
  • Convert the color to OKLCH and reduce the chroma and lightness. This keeps the origin hue but is a little slower to render.

Chris Lilley has created a nice comparison between different gamut mapping methods.

The CSS Colors 4 spec requires browsers to use the OKLCH method for gamut mapping. But still, right now, Safari uses the fast, but inaccurate, clipping method. That’s why we currently recommend manual gamut mapping and adding both sRGB and P3 colors to CSS:

.martian {
  background:   oklch(69.73% 0.155 112.79);
}
@media (color-gamut: p3) {
  .martian {
    background:   oklch(69.73% 0.176 112.79);
    /* You'll only see the preview using Safari with P3 monitors */
  }
}

And here’s some good news: oklch() polyfills can do this for you. They automatically wrap P3-colors with @media and set the closest sRGB-colors as fallbacks.

How to add OKLCH to your project

Step 1: Adding OKLCH polyfill to CSS

As of October 2022, only Safari supports oklch(). Thankfully, the color function is easy to polyfill for static values.

There are two polyfills which support oklch():

It’s very likely that you already have postcss-preset-env on your system. For instance, every Create React App project has it.

  1. Check your lock file (package-lock.json, yarn.lock or pnpm-lock.yaml) for postcss-preset-env. Be sure that it uses the latest version: 7.x or above.
  2. Add oklch(100% 0 0) to your CSS and see if it will be compiled to rgb() by your build tool.

If you don’t have postcss-preset-env, but have a front-end build tool (like webpack):

  1. Install postcss-preset-env using your package manager. For npm, run:
    npm install postcss-preset-env postcss
  2. Check the PostCSS docs to see how you should add PostCSS support to your build tool. For instance, webpack needs postcss-loader but Vite supports it out of the box.
  3. If you already have PostCSS integration, look for the PostCSS config. Many projects already use PostCSS (for instance, for Autoprefixer). Look for postcss.config.js or .postcssrc.json in the project root and then the "postcss" section in package.json or postcss in build tool config.
  4. If you were able to locate the PostCSS config, add postcss-preset-env to plugins:
    {
      "plugins": [
    +   "postcss-preset-env",
        "autoprefixer"
      ]
    }
  5. If you didn’t find the config, create a .postcssrc.json file in the project root:
    {
      "plugins": [
        "postcss-preset-env"
      ]
    }

If you don’t have a build tool, we recommend using Vite or compiling your CSS with the lightningcss CLI.

Add .test{ background: oklch(100% 0 0) }, compile the CSS, then check the output CSS for .test{background:#fff}.

Step 2: Converting currently existing colors

Once you have the oklch() polyfill, you can replace all colors using hex, rgb() or hsl() formats to OKLCH; they’ll work in every browser.

Search for any colors in your CSS source code and convert them to oklch() using the OKLCH convertor.

.header {
- background: #f3f7fa;
+ background: oklch(97.4% 0.006 240);
}

You may also use this script to automatically convert all the colors:

npx convert-to-oklch ./src/**/*.css

Note: these polyfills only work in CSS, they will not work for HTML or JS sources.

Extra: Adding a color palette

Perhaps this little bit of refactoring is also a good time to increase your CSS code’s maintainability by moving the colors onto a palette:

These are requirements for color palettes:

  • All colors are described as CSS Custom Properties.
  • React/Vue/etc. components only use these colors as var(--error).
  • Designers should try to re-use colors to reduce number of color variations.
  • For a dark or high-contrast theme, you do not need @media in your components’ CSS, you just change CSS Custom Properties in the palette.

Here’s an example of this approach.

:root {
  --surface-0: oklch(96% 0.005 300);
  --surface-1: oklch(100% 0 0);
  --surface-2: oklch(99% 0 0 / 85%);
  --text-primary: oklch(0% 0 0);
  --text-secondary: oklch(54% 0 0);
  --accent: oklch(57% 0.18 286);
  --danger: oklch(59% 0.23 7);
}

@media (prefers-color-scheme: dark) {
  :root {
    --surface-0: oklch(0% 0 0);
    --surface-1: oklch(29% 0.01 300);
    --surface-2: oklch(29% 0 0 / 85%);
    --text-primary: oklch(100% 0 0);
  }
}

And plus, moving over to oklch() will be a little easier after palette creation.

Step 3: Maintaining OKLCH with Stylelint

Stylelint is a style linter that’s useful for finding common mistakes and promoting best practices. It’s like ESLint, but for CSS, SASS, or CSS-in-JS.

Stylelint can be very useful when migrating to oklch() because you can:

  • Specify that colors using hex, rgb(), hsl() will not be used and instead keep all the colors in oklch() to improve consistency.
  • Double-check that all P3 colors are inside @media (color-gamut: p3) to avoid browser gamut correction (right now, Safari doesn’t do this correctly).

Let’s install Stylelint and the stylelint-gamut plugin using your package manager. With npm, run:

npm install stylelint stylelint-gamut

Create .stylelintrc config with:

{
  "plugins": [
    "stylelint-gamut"
  ],
  "rules": {
    "gamut/color-no-out-gamut-range": true,
    "function-disallowed-list": ["rgba", "hsla", "rgb", "hsl"],
    "color-function-notation": "modern",
    "color-no-hex": true
  }
}

Add the Stylelint call to npm test to run it on CI. Change package.json like so:

  "scripts": {
-   "test": "eslint ."
+   "test": "eslint . && stylelint **/*.css"
  }

Run npm test to find any colors which should be converted to oklch().

We also recommend adding the stylelint-config-recommended to .stylelintrc. This Stylelint sharable config will ensure that your CSS code is using the popular best practices.

Extra: P3 colors

Replacing colors with oklch() will improve code readability and maintainability, but it will not add new features for users. However, there is an additional feature of OKLCH which will be visible to users: we can add rich, wide-gamut P3 colors to our websites. For instance, we could add deep colors to a landing page.

Here’s how to do it:

  1. In your CSS, choose some saturated color, like an accent color.
  2. Copy it into OKLCH Color Picker.
  3. Change the Chroma and Lightness values to move the color into the P3 area. The Lightness chart will provide the best feedback. Simply move the color above the thin white line.
  4. Copy the result and wrap it with a color-gamut: p3 media query.
  :root {
    --accent:   oklch(70% 0.2 145);
  }
+ @media (color-gamut: p3) {
+   :root {
+     --accent:   oklch(70% 0.29 145);
+   }
+ }

Extra: OKLCH in SVG

You can use OKLCH, not only in CSS, but also in SVGs (or HTML). For instance, this could be useful for adding unique, rich colors to app icons.

Note: there are no polyfills for SVG usage, so we recommend using the oklch() function only when setting wide-gamut P3 colors.

<svg viewBox="0 0 120 120" xmlns="http://www.w3.org/2000/svg">
  <style>
    @media (color-gamut: p3) {
      rect {
        fill:   oklch(55% 0.23 146)
      }
    }
  </style>
  <rect x="10" y="10" width="100" height="100"
        fill="   #048c2c" />
</svg>

Extra: OKLCH/Oklab in gradients

A gradient is a path through a color space between 2 or more dots. This means that if you change your color space, you’ll end up with a very different gradient for the same starting and ending colors.

There are four squares. Each square shows the code for gradients with sRBG, Oklab, and OKLCH. The code in each block is the same, but for each color space, the gradient is slightly different.

Gradients in different color spaces

For gradients, there is no silver bullet; different tasks will require a different color space. But the Oklab color space (OKLCH’s sister that lives on top of cartesian coordinates) often has good results:

  • It has no grayish area in the middle as default (sRGB) gradients.
  • It has not blue-to-purple shift as Lab.

CSS Image 4 specification has a special syntax to change the color space in gradients:

.oklch {
	background: linear-gradient(in lab, blue, green);
}

It only works in Safari Technological Preview. You can use the PostCSS plugin to polyfill it for use right now.

Extra: Color modification with OKLCH

We’ll finally be able to see the true power of OKLCH once more browsers begin to support native CSS color modification (relative colors) from CSS Colors 5. OKLCH is incredibly good for color modification: unlike HSL, it has predicted contrast, and unlike LCH, it doesn’t have any problems with hue shifts upon chroma changes.

Unfortunately, this feature can not be polyfilled with full support for dynamic CSS Custom Properties. Nevertheless, it’s a good idea to familiarize yourself with OKLCH axes today in order to be ready for tomorrow!

Here’s how you’ll be able to define a 10% darker :hover background for a button:

.button {
  background:   var(--accent);
}
.button:hover {
  background:   oklch(from var(--accent) calc(l - 10%) c h);
}

With CSS Custom Properties, we can define the :hover logic just once and then create many variants simply by changing the source color.

.button {
  --button-color:   var(--accent);
  background: var(--button-color);
}
.button.is-secondary {
  --button-color:   var(--dimmed);
}
.button.is-error {
  --button-color:   var(--error);
}
.button:hover {
  /* One :hover for normal, secondary, and error states */
  background: oklch(from var(--button-color) calc(l + 10%) c h);
}

Thanks to OKLCH’s predictable contrast, we can work with colors from user input and have good a11y on our sites.

.header {
  /* JS will set --user-avatar-dominant */
  background: oklch(from var(--user-avatar-dominant) 80% 0.17 h);
  /* With OKLCH, we're sure that black text will be always readable
     on any hue, since we set L to 80% */
  color: black;
}

And here’s one more benefit worth mentioning: OKLCH will be able to fully generate design system palettes in CSS.

Extra: OKLCH in JS

You don’t need to wait for CSS Colors 5 in order to use OKLCH for color modification.

With Color.js or culori, you can transform colors in JS while reaping all the benefits of OKLCH color space. You can check examples with culori using the OKLCH Color Picker source code. In this article, I’ll use Color.js.

Here’s an example that shows off making an accent color from a custom color:

import Color from 'colorjs.io'

// Parse any CSS color
let accent = new Color(userAvatarDominant)

// Set lightness and contrast
accent.oklch.l = 0.8
accent.oklch.c = 0.17

// Gamut mapping to sRGB if we are out of sRGB
if (!accent.inGamut('srgb')) {
  accent = accent.toGamut({ space: 'srgb' })
}

// Make the color 10% lighter
let hover = accent.clone()
hover.oklch.l += 0.1

document.body.style.setProperty('--accent', accent.to('srgb').toString())
document.body.style.setProperty('--accent-hover', hover.to('srgb').toString())

You can use these libraries to generate an entire design system palette in the OKLCH color space. This allows you to have predicted contrast and better accessibility. As an example of this in practice, Huetone, an accessible palette generator, uses Oklab by default.

Summing why we moved to OKLCH

At our company, we already use OKLCH in our projects—as a matter of fact, the website you’re on right now uses oklch(), too. So, here’s the question of the moment: what benefits have we gained after moving to OKLCH?

1. Better readability

With OKLCH, we can understand colors just by looking at code.

For instance, we can compare darkness in the code and find contrast-related accessibility issues:

.text {
  /* ERROR: a 20% lightness difference is not sufficient for good contrast and a11y */
  background:   oklch(80% 0.02 300);
  color:   oklch(100% 0 0);
}

.error {
  /* ERROR: colors have a slightly different hue */
  background:   oklch(90% 0.04 30);
  color:   oklch(50% 0.19 27);
}

2. Simple color modifications

We can apply simple color modifications right in the code and get predictable results:

.button {
  background:   oklch(50% 0.2 260);
}
.button:hover {
  background:   oklch(60% 0.2 260);
}

3. P3 colors

We can use the same color functions for both sRGB and P3 wide-gamut colors.

.buy-button {
  background:   oklch(62% 0.19 145);
}
@media (color-gamut: p3) {
  .buy-button {
    background:   oklch(62% 0.26 145);
  }
}

4. Better communication with design teams

Since OKLCH is much closer to real-life color, using oklch() in CSS will educate developers and lead the community to an overall better understanding of color.

Further, this could have larger ramifications: one small step towards improving communication between development and design teams.

Modern design tools (like palette generators) use Oklab or Lab for better accessability. Using the same oklch() in both designer tools and developer CSS will keep everyone on the same page.

5. We’re ready for the future

By moving to OKLCH today, we’re preparing ourselves for the not-so-distant future where native color modification will be available in CSS. OKLCH is the best color space for color transformations and it’s better to become familiar with its axes by using them in color definitions now.

.button:hover {
  background: oklch(from var(--button-color) calc(l + 10%) c h)
}

Thanks for reading! Speaking of the future, if you need help getting ready for your future, Evil Martians can help! We work with startups and established businesses—and we get things done, including: Ruby on Rails, product design, real-time applications, and so much more. If you have a project in need, get in touch with our team!

In the same orbit

Contact us

We’d love to hear from you! We’re not really all that evil, and we love discussing potential projects, intriguing ideas, and new opportunities. Complete the form below or drop us a line at surrender@evilmartians.com.

Martians at a glance
16
years in business

A product development consultancy that works with startups and established businesses, while also creating open source-based products and services