The "contrast" set leads with the family's own tone and its
interaction complement – the two colours of the title plate (red and gold
for the red family) – then the complementary family (blue), the family at
another lightness, the complementary family at another lightness, and a
warm neutral. With mode = "dark" each slot keeps its hue (only its
lightness changes), so a category keeps its colour when the page switches
theme.
Adjacent levels differ in hue, so a two-group comparison is always legible. The "family" set is the single-hue A900-A300 ramp.