Healthful Slab Sky

Old English hǣlth, health — adjectival suffix -ful. As a color modifier, healthful implies a clear-and-vital-and-wholesome quality where the hue carries the visual register of fresh-air-and-sunlight outdoor health-promoting environment. Sits at the crisp-and-wholesome end of the grid, parallel to salubrious and wholesome in usage.

Old French esclape, splinter / slab. As a color modifier, slab implies a flat-thick-stone-or-wood quality, the visual register of Cotswold-and-Yorkshire-flagstone-and-slab hand-quarried-and-flat-thick stone-and-timber-and-marble hand-quarried-flat-thick-slab surfaces under Cotswold-and-Yorkshire flagstone-and-slab quarry-light. Sits at the modifier-and-texture end of the grid, parallel to plate and tile 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.