Seed color

A seed colour is an input, not a swatch you ship. You hand the generator one value and it produces the rest: a ramp of lightness steps at that hue, a set of neutrals tinted towards it, and the role assignments that say which step is a button fill and which is the tinted background behind a notice. Nothing downstream names the seed. Components ask for the roles, so changing the one input re-derives every surface at once instead of sending someone through a stylesheet replacing hex codes.

The reason this works is that the generator does its arithmetic in a perceptual space. Material’s HCT holds hue and chroma from CIELAB and takes its tone axis from a contrast model, so tone 40 against tone 100 lands on a known contrast whatever hue arrived, and other tools do the same job in OKLCH. Because the lightness ladder is fixed and only the hue is unpredictable, an arbitrary seed still produces an accessible scheme. That is the whole trick, and it is why the rungs are usually numbered: “step 11 on step 2” is a rule that survives a change of seed, while “this blue on that grey” is not.

Where the seed comes from is the interesting part. Usually it is the brand colour, carried in once and then left alone. It can also be extracted from an image, which is what Material You does when it reads source colours out of a wallpaper and every app on the device shifts together. Some systems take more than one: a secondary or tertiary seed for accents that should not simply be the primary hue rotated, and a neutral seed that decides how warm the greys are.

Two cautions. A seed is a starting point, not a guarantee: generated ramps drift at the extremes, near-neutral and very light seeds behave badly, and any serious system checks the output and pins overrides rather than trusting the curve. And a generated scheme has no opinion about meaning, so anything carrying a fixed sense of its own, a status colour, a chart’s categorical series, an illustration, needs its own answer before the seed decides for it.