Useful Rigel Teal

Latin ūsus, use — adjectival suffix -ful. As a color modifier, useful implies a clear-and-purpose-serving quality where the hue carries the visual register of helpful-and-supporting design-element. Sits at the crisp-and-functional end of the grid, parallel to practical and serviceable in usage.

Arabic rijl-al-jawzā', foot-of-Orion. As a color modifier, rigel implies a blue-supergiant-and-Orion-foot quality, the visual register of Orion-Hunter-and-winter-blue-supergiant-Rigel hand-blue-supergiant-and-Orion-foot Orion-Hunter-and-winter-blue-supergiant-and-Bortle-1 rigel-and-blue-supergiant-and-winter-zenith surfaces under Orion-Hunter-and-winter-blue-supergiant-and-Bortle-1 January-and-February-winter-Orion deep-blue-stellar-light. Sits at the modifier-and-cosmic end of the grid, parallel to vega and deneb in usage.

Anas crecca, the small dabbling duck whose male in breeding plumage sports a chestnut head crossed by a glossy green-blue stripe. The color refers to that stripe — the iridescent panel just behind the eye: a saturated, slightly muted blue-green with the optical depth of structural color rather than pigment. Cooler than cypress, warmer than cerulean, with the ornithological specificity of a color named for one feather of one bird.