Material colour palette generator

Builds a tonal scale from a seed colour — the structure Material Design uses, where a single colour becomes a ladder of tones referenced by number rather than by name.

The insight behind Material’s system is that naming colours "primary-light" and "primary-dark" stops working as a system grows, whereas numbered tones scale indefinitely and make contrast predictable: if tone 10 and tone 90 always have sufficient contrast, any pair chosen by that rule is safe without checking each one. Material 3 builds its tones in a perceptual space rather than in HSL, so the steps are visually even; the scale here is built in HSL and is numerically even, which looks slightly less uniform at the extremes. For a real Material implementation, the official tooling generates the full tonal palette from a seed.