Useful Virgo Sky

Latin ūsus, use — adjectival suffix -ful. As a color modifier, useful implies a clear-and-purpose-serving quality where the hue carries the visual register of helpful-and-supporting design-element. Sits at the crisp-and-functional end of the grid, parallel to practical and serviceable in usage.

Latin virgo, virgin-or-maiden-of-the-zodiac. As a color modifier, virgo implies a maiden-and-earth-sign-and-Mercury-ruled-mutable-earth quality, the visual register of Hellenic-Virgo-and-Astraea-maiden hand-maiden-and-earth-sign-and-Mercury-ruled-mutable-earth Hellenic-Virgo-and-Astraea-maiden-and-Spica-grain virgo-and-maiden-and-earth-sign surfaces under Hellenic-Virgo-and-Astraea-maiden-and-Spica-grain late-summer-and-August-and-September mutable-earth-sign-light. Sits at the modifier-and-zodiac end of the grid, parallel to leo and libra 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.