Giving each of ten sites its own brand color makes them look like a colorful collection by one operator. An early approach did exactly that with a color per site and contrast fixing, and it was retired by the decision to remove bright colors. Now color comes from the design pack, and sites do not create colors.
This is kept by structure rather than by a machine check. Color values live in one place in each pack, and the command that creates a new site (new:site) does not make a color. Sites must still be distinguishable, so that is done with three things: the site name, a two-letter monogram drawn in the pack’s font, and the combination of component variants. In the “Other parenting sites” list on the right, names and marks differ but the color is the same everywhere.
This does not mean packs share colors. Accent colors differ between packs (KRDS, Primer and Carbon lean blue; shadcn is near-black). The promise is that once a pack is chosen, all ten sites share one color system.
When to use
Think of it when making a new site and wanting “a color of its own.” Refine the name, pick the two-letter mark and vary the variants instead.