OKLCH

OKLCH is a colour space expressing a colour as lightness, chroma, and hue, built on the Oklab model. Its defining property is perceptual uniformity: equal numeric steps correspond to roughly equal perceived differences, which is emphatically not true of the older sRGB or HSL representations.

That property is what makes it useful for design systems. In HSL, holding lightness constant while changing hue produces colours that look wildly different in brightness — yellow at fifty percent lightness is far brighter than blue at fifty percent. Building a palette in HSL therefore requires hand-correcting every hue. In OKLCH, a lightness ramp reads as a lightness ramp across the whole hue circle, so a systematic palette can be generated rather than tuned.

It also handles wide-gamut displays. OKLCH can express colours outside sRGB, with well-defined behaviour when clamping into a narrower gamut, which matters as displays outgrow the old standard.

The practical caution is that perceptual uniformity is not the same as contrast compliance. Two colours with equal OKLCH lightness may still fail an accessibility contrast ratio, because that ratio is computed from relative luminance under a different formula. Use OKLCH to build the ramp and a contrast check to validate the pairs; see Color Contrast.