Vitreous Cliff Sky

Latin vitreus, glass-like — derived from vitrum (glass). As a color modifier, vitreous implies a clear-and-glassy quality where the hue carries the optical clarity of polished crown-glass. Sits at the crisp-and-clear end of the grid, parallel to pellucid and crystalline in usage.

Old English clif, steep face of rock. As a color modifier, cliff implies a vertical-and-weathered quality, the visual register of Cornish-coast-and-Yorkshire sea-cliff sandstone-and-granite headland-face surfaces standing against open sky and salt-air in late-afternoon raking light. Sits at the modifier-and-place end of the grid, parallel to bluff and crag 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.