Healthful Scud 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.

Origin obscure, low-fast-driven-cloud. As a color modifier, scud implies a low-fast-driven-cloud-and-storm-front quality, the visual register of North-Sea-and-Cornish-coast-scud hand-low-fast-driven-cloud-and-storm-front North-Sea-and-Cornish-coast-scud-and-Atlantic-front-cloud scud-and-low-fast-driven-cloud surfaces under North-Sea-and-Cornish-coast-scud-and-Atlantic-front-cloud Lizard-Point-and-Outer-Hebrides storm-front-cloud-light. Sits at the modifier-and-weather end of the grid, parallel to gust and mistral 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.