Why oklch

HSL looks perceptually uniform but isn’t. An hsl(60, 100%, 50%) yellow and an hsl(240, 100%, 50%) blue share the same L value (50%), but the yellow looks dramatically lighter. If you try to build a lightness scale with HSL, you end up hand-tuning every hue to compensate.

oklch isn’t harder to read than hsl once you internalise three numbers: L (how bright, 0–1), C (how vivid, 0–0.4), H (which colour, 0–360). And it gives you something hsl can’t: the guarantee that your lightness scale actually looks even.