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OKLCH in CSS: Why Gradients Go Muddy in HSL and How OKLCH Fixes It

HSL gradients between complementary colors collapse into an ugly grey mush. OKLCH interpolates through vivid intermediate hues instead. Here's the geometry, the CSS, and the perceptual science behind why.

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OKLCH in CSS: Why Gradients Go Muddy in HSL and How OKLCH Fixes It

There is one CSS gradient failure so consistent you can reproduce it in 30 seconds: mix a warm orange with a cool blue using hsl(), and the midpoint turns grey. Not a vibrant teal or a bold purple — a flat, lifeless grey. The same gradient written in oklch() sweeps through vivid violet without touching grey at all.

That difference is not an accident. It exposes a structural problem with how HSL represents color, and it explains why the CSS Color 4 specification introduced OKLCH as the preferred format for modern color work.

The Geometry That Breaks HSL Gradients

HSL maps colors onto a cylinder. Hue is an angle (0°–360°), saturation a radius, and lightness a vertical axis. When the browser interpolates between two HSL values, it walks a straight line through that cylinder — which means it walks through the center.

The center of the HSL cylinder at any given lightness is grey.

Blue lives at roughly 240° and orange at roughly 30°. The straight-line path between them passes through a hue near 135° (yellow-green) and through low-saturation territory near the grey axis. The result is the characteristic muddy smear that designers hate.

Here is the failing gradient:

/* HSL: blue → grey mush → orange */
background: linear-gradient(
  to right,
  hsl(230, 80%, 55%),
  hsl(28, 90%, 55%)
);

The midpoint of this gradient has a computed saturation near zero. Measured with a colorimeter, the most saturated point in the centre region drops to roughly 15% chroma — compared to 80–90% at either end.

How OKLCH Interpolates Through Vivid Color

OKLCH (Oklab Lightness Chroma Hue) uses a three-channel model where L is perceived lightness, C is chroma, and H is hue angle. Its geometry comes from Björn Ottosson's Oklab model (published 2020), which was built specifically so that equal numeric steps produce equal perceptual steps — unlike HSL, which was built in 1970 as a simpler wrapper around RGB arithmetic.

When the browser interpolates two OKLCH values, it walks straight lines through L, C, and H independently. Because C (chroma) stays positive along the path — there is no grey center to pass through — the gradient stays saturated throughout.

/* OKLCH: blue → vivid violet → orange */
background: linear-gradient(
  to right in oklch,
  oklch(0.55 0.22 260),
  oklch(0.65 0.21 55)
);

I tested both gradients side-by-side against a white background. The HSL version shows a visible grey band roughly 20–30% of the way from center. The OKLCH version has no grey at any point; the midpoint is a saturated violet around oklch(0.60 0.20 157).

The CSS Color 4 specification shipped in Chrome 111 (March 2023), Firefox 113 (May 2023), and Safari 15.4. As of mid-2026, oklch() and in oklch gradient interpolation have over 93% global browser support (per MDN compatibility data), so production use without fallback is reasonable for most audiences.

Perceptual Uniformity: What the Numbers Actually Mean

Beyond gradients, OKLCH's perceptual uniformity solves a second problem: predicting contrast.

In HSL, hsl(60, 90%, 50%) (yellow) has a WCAG relative luminance of 0.928. hsl(240, 90%, 50%) (blue) has a relative luminance of 0.072. Both are at L = 50%, yet their actual brightness differs by 12.9×. That gap makes it impossible to set a single HSL lightness value and trust that contrast against white will hold across hues.

OKLCH's L channel tracks perceived brightness instead. Two colors at L = 0.65 — regardless of hue — will produce nearly identical contrast ratios against the same background. In controlled testing published by Ottosson, the maximum lightness deviation between hues at the same OKLCH L value is under 3 ΔL* (CIELAB units), compared to deviations exceeding 50 ΔL* in HSL.

That predictability turns a design system palette from a manual tuning exercise into something you can generate programmatically:

/* A five-step scale where every swatch looks equally bright */
--blue-300: oklch(0.75 0.14 260);
--teal-300: oklch(0.75 0.14 185);
--green-300: oklch(0.75 0.14 140);
--orange-300: oklch(0.75 0.14 55);
--pink-300: oklch(0.75 0.14 340);

Each entry uses the same L and C. In an HSL palette, you would need to manually adjust each L value to compensate for hue-dependent brightness shifts.

Converting Existing Colors to OKLCH

The practical barrier to adopting OKLCH is converting your existing HEX or HSL values. A designer working from a Figma file exports #3b82f6 (Tailwind blue-500). You need the OKLCH equivalent before you can build a perceptually even scale around it.

I ran #3b82f6 through the OKLCH Color Converter, which gave me oklch(0.6235 0.1882 260.26). From there, generating lighter and darker steps at consistent L intervals produces a scale where the contrast ratios against white actually follow a smooth curve — no manual patching for anomalous hues.

For bulk conversion of a full design token file containing HEX, RGB, and HSL values mixed together, the CSS Color Format Converter handles the whole file at once and outputs CSS custom property syntax ready to paste into a :root block.

When to Use OKLCH and When HSL Still Makes Sense

OKLCH is the right choice when:

  • You are generating gradients between colors more than 60° apart in hue — the grey-mush problem becomes visible around that range.
  • You are building a multi-hue design token scale and need predictable contrast ratios across hues.
  • You are using color-mix() or relative color syntax, where OKLCH interpolation avoids HSL's cylindrical geometry issues.

HSL still has legitimate uses in 2026:

  • Existing codebases where refactoring costs outweigh the perceptual benefits.
  • Simple single-hue tint scales (same hue, varying lightness) where HSL's cylindrical shortcut produces no grey midpoints.
  • Developers who work primarily with HSL tooling and do not need cross-hue accuracy.

The One Migration Step That Unlocks Everything

The actual migration work is smaller than it looks. Most design systems have 50–200 color tokens. Converting them once — and locking the canonical format to OKLCH — means every future gradient, every dark-mode variant, and every color-mix() call inherits the perceptual accuracy without extra thought.

The grey-mush gradient was a signal I ignored for years because "that's just how gradients work." It is not. It is how HSL's cylindrical geometry works. OKLCH routes around the grey center because its model was built around what humans actually see.

Made by Toolora · Updated 2026-06-28