Sterile Day Sky

Latin sterilis, barren / not-fertile — sharing root with Greek steiros (barren). As a color modifier, sterile implies a clear-and-medical-clean-and-stripped quality, the crisp color of operating-theater surgical-environment white-and-stainless-steel surfaces. Sits at the crisp-and-clean end of the grid, parallel to sanitary and hygienic in usage.

Old English dæg, daylight period. As a color modifier, day implies a midday-and-broad-daylight quality, the visual register of Mediterranean-and-temperate mid-day full-sun atmospheric clarity-and-shadow open-sky working-and-walking surfaces under noon-day overhead light. Sits at the modifier-and-time end of the grid, parallel to noon and morn in usage.

The blue of a clear sky at noon — produced by Rayleigh scattering, the preferential dispersion of shorter wavelengths through atmospheric molecules. Air itself is colorless; the color we see is sunlight scattered toward our eyes by every cubic kilometer above. The reference shade is mid-latitude noon under a high pressure system: a clean, slightly green-shifted blue with the luminous depth of light scattered across an entire hemisphere of air.