Healthful Prowl 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.

Middle English prollen, to-roam-and-search. As a color modifier, prowl implies a stalking-and-hunting-and-watchful quality, the visual register of panther-and-tiger-prowl hand-stalking-and-hunting-and-watchful panther-and-tiger-and-leopard prowled-and-stalking-and-hunting-and-watchful surfaces under panther-and-tiger-and-leopard jungle-and-savanna-and-night-forest big-cat-light. Sits at the modifier-and-mood end of the grid, parallel to stalk and lurk 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.