Colour that can be reasoned about.

In hex and HSL, lightness is a lie. Two colours with the same nominal lightness can differ enormously in how bright they appear, because the notation describes the signal sent to the display rather than the impression made on a person. Yellow at 50% reads far lighter than blue at 50%.

OKLCH is perceptual: its lightness channel tracks apparent brightness. That single property is what makes everything else on this page possible. A hue can be changed without silently changing how light it reads, a whole family can be darkened by a known amount, and a contrast budget becomes arithmetic instead of trial and error.

Components never name a hue. They ask for a role — the surface a card sits on, the text colour for secondary information, the accent that means "act here" — and the token layer answers with a value appropriate to the active theme.

The gain is not tidiness. It is that a role can be re-measured, and a hue cannot. When every foreground names the surface it belongs to, the set of pairs that must clear a contrast floor is derivable rather than remembered, which is exactly how the evidence page builds itself.

The badge idiom — coloured text on a soft wash of the same hue — hides a trap. The wash moves the background toward the text, so a colour that comfortably clears the contrast floor on a plain card can fall below it on a 12% tint of itself. The pairing looks correct in isolation and fails in composition.

The system's answer is a parallel set of tokens for exactly this case. Where a hue is used as a badge, its text takes the -on-tint variant — the same colour pulled far enough away from its own wash to clear the floor over the composite.