There’s been a lot of exciting work in the CSS color specifications lately, and the new features are starting to land in browsers – so we’ve been preparing to add support in Sass as well.

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Sass Color Spaces

Support for new CSS color spaces in Sass

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note [Sep 21, 2022]:

A first draft of the proposal is complete, and posted for public feedback.

I’m very excited about this. It will allow us to:

Read the proposal & request for comment »

Some CSS Background

Historically CSS has been limited to a single color model (RGB) and gamut (sRGB). Authors have various formats to describe colors in that gamut – using cubic hex notation (#rgb/#rrggbb/#rrggbbaa) and functions (rgb()/rgba()), or cylindrical functions (hsl()/hwb()) that give us a handy polar-axis hue.

Unfortunately, sRGB is a relatively narrow color gamut, and RGB isn’t a perceptually uniform color-model. Many monitors (and some browsers) now support wider color gamuts (such as the popular display-p3), and there has also been significant progress in developing more perceptually uniform color spaces such as CIE LAB and okLAB.

CSS Colors level 4 & level 5 define CSS access to these newer gamuts & formats, along with tools for mixing and adjusting colors. We plan to support all the new CSS functions in Sass, along with some additional functions for inspecting and manipulating colors before they reach the browser. This required rethinking the Sass color module from the ground up.

Standard CSS Color Functions

oklab() and oklch()

The oklab() (cubic) and oklch() (cylindrical) functions provide access to an unbounded gamut of colors in a perceptually uniform space. Authors can use these functions to define reliably uniform colors. For example, the following colors are perceptually similar in lightness and saturation:

$pink: oklch(64% 0.196 353); // hsl(329.8 70.29% 58.75%)
$blue: oklch(64% 0.196 253); // hsl(207.4 99.22% 50.69%)

The oklch() format uses consistent “lightness” and “chroma” values, while the hsl() format shows dramatic changes in both “lightness” and “saturation”. As such, oklch is often the best space for consistent transforms.

lab() and lch()

The lab() and lch() functions provide access to an unbounded gamut of colors in a space that’s less perpetually-uniform but more widely-adopted than OKLab and OKLCH.

hwb()

Sass now supports a top-level hwb() function that uses the same syntax as CSS’s built-in hwb() syntax.

color()

The new color() function provides access to a number of specialty spaces. Most notably, display-p3 is a common space for wide-gamut monitors, making it likely one of the more popular options for authors who simply want access to a wider range of colors. For example, P3 greens are significantly ‘brighter’ and more saturated than the greens available in sRGB:

$fallback-green: rgb(0% 100% 0%);
$brighter-green: color(display-p3 0 1 0);

Sass will natively support all predefined color spaces declared in the Colors Level 4 specification. It will also support unknown color spaces, although these can’t be converted to and from any other color space.

New Sass Color Functions

color.channel()

This function returns the value of a single channel in a color. By default, it only supports channels that are available in the color’s own space, but you can pass the $space parameter to return the value of the channel after converting to the given space.

$brand: hsl(0 100% 25.1%);

// result: 25.1%
$hsl-lightness: color.channel($brand, "lightness");

// result: 37.67%
$oklch-lightness: color.channel($brand, "lightness", $space: oklch);

color.space()

This function returns the name of the color’s space.

// result: hsl
$hsl-space: color.space(hsl(0 100% 25.1%));

// result: oklch
$oklch-space: color.space(oklch(37.7% 38.75% 29.23deg));

color.is-in-gamut(), color.is-legacy()

These functions return various facts about the color. color.is-in-gamut() returns whether the color is in-gamut for its color space (as opposed to having one or more of its channels out of bounds, like rgb(300 0 0)). color.is-legacy() returns whether the color is a legacy color in the rgb, hsl, or hwb color space.

color.is-powerless()

This function returns whether a given channel is “powerless” in the given color. This is a special state that’s defined for individual color spaces, which indicates that a channel’s value won’t affect how a color is displayed.

$grey: hsl(0 0% 60%);

// result: true, because saturation is 0
$hue-powerless: color.is-powerless($grey, "hue");

// result: false
$hue-powerless: color.is-powerless($grey, "lightness");

color.same()

This function returns whether two colors will be displayed the same way, even if this requires converting between spaces. This is unlike the == operator, which always considers colors in different non-legacy spaces to be inequal.

$orange-rgb: #ff5f00;
$orange-oklch: oklch(68.72% 20.966858279% 41.4189852913deg);

// result: false
$equal: $orange-rgb == $orange-oklch;

// result: true
$same: color.same($orange-rb, $orange-oklch);

Existing Sass Color Functions

color.scale(), color.adjust(), and color.change()

By default, all Sass color transformations are handled and returned in the color space of the original color parameter. However, all relevant functions now allow specifying an explicit color space for transformations. For example, lightness & darkness adjustments are most reliable in oklch:

$brand: hsl(0 100% 25.1%);

// result: hsl(0 100% 43.8%)
$hsl-lightness: color.scale($brand, $lightness: 25%);

// result: hsl(5.76 56% 45.4%)
$oklch-lightness: color.scale($brand, $lightness: 25%, $space: oklch);

Note that the returned color is still emitted in the original color space, even when the adjustment is performed in a different space.

color.mix()

The color.mix() function will retain its existing behavior for legacy color spaces, but for new color spaces it will match CSS’s “color interpolation” specification. This is how CSS computes which color to use in between two colors in a gradient or an animation.

Deprecations

A number of existing functions only make sense for legacy colors, and so are being deprecated in favor of color-space-friendly functions like color.channel() and color.adjust():

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