Heavy Castor Indigo

Old English hefig, weighty — cognate with heave. Used as a color modifier since at least the seventeenth century to indicate weight in saturation as much as value: heavy with pigment, heavy-bodied. In the engine's adjective grid, heavy sits alongside deep and plush in the dark-and-saturated quadrant. Closer to a fabric description than a pure value word.

Greek Κάστωρ, Gemini-twin-and-horseman. As a color modifier, castor implies a Gemini-twin-and-mortal-brother quality, the visual register of Gemini-Castor-and-Pollux-twin hand-Gemini-twin-and-mortal-brother Gemini-Castor-and-Pollux-twin-and-Argonaut castor-and-Gemini-twin-and-mortal-brother surfaces under Gemini-Castor-and-Pollux-twin-and-Argonaut spring-Gemini-and-Bortle-1-sky stellar-twin-light. Sits at the modifier-and-cosmic end of the grid, parallel to pollux and spica in usage.

Indigofera tinctoria, the South Asian legume whose leaves yield the deep blue dye that has clothed humanity for at least four thousand years — Egyptian linen, Mayan textile, the slave-grown plantations of Carolina. The color refers to a freshly indigo-dyed cotton thread: a saturated, slightly violet-shifted deep blue with the slight lustre of a fiber surface oxidized in air. Deeper than cobalt, cooler than royal.