Colour
Three reds, a gold and a cool gray family. The reds are grounds and never button fills; the gold is the button fill and never sets type. Keeping those two rules is what stops the palette collapsing into mud.
The primary ground and the heaviest thing in the system: 16.2:1 against white. Heroes, the footer, and any band that has to feel institutional. White display type sits on it well; nothing else does.
The second band, for the section that follows a maroon one. Lighter and warmer, so a run of three bands reads as a progression rather than a repetition. It is also the link colour on every light ground — 8.91:1 on white — where gold cannot go.
The button fill, and the third band. It does not work as type: 3.01:1 on white and 2.40:1 on gainsboro, both below AA at any size — so a link on a light ground is wine, and gold type is reserved for dark bands, where it reaches 5.38:1. Anything set on a gold ground is maroon, including a button label.
The occasional fourth, for a card or a highlight inside a band. It is the palette’s trap: close enough to the error colour to be confused with it, so it never carries a message.
Errors and destructive confirmations. Added, not inherited: the reference site gives error and success messages the same plain black, so it has no error colour to lift. With three reds already in the palette, hue cannot separate this one — chroma does. Every brand red is muted (0.10–0.14 in oklch); Alarm is vivid at 0.19, which is what makes it read as an alert rather than as decoration. 6.57:1 on white, 5.23:1 on gainsboro.
One hard limit: Alarm on maroon is 2.47:1 and fails. An error may never appear inside a maroon band — move the form to gainsboro or white, or the message will be unreadable exactly when it matters.
Headings on light
All running text
Captions, secondary bands
Meta, disabled, sheet labels
The light ground and every rule
The neutrals lean cool and slightly blue while the grounds are warm. That opposition is deliberate: a warm gray next to maroon goes muddy, and a cool one keeps its distance.