Plain Gaul Sky

Latin planus, flat, level — used as a color modifier since the medieval period for hues that read as undecorated and direct. Plain white, plain blue: moderate saturation, no shift, no surface effect. Sits in the crisp-bucket center, with the implication of restraint rather than absence.

Latin Gallia, Gaul. As a color modifier, gaul implies a pre-Roman-French-Celtic quality, the visual register of Gallia-Belgica-and-Gallia-Aquitania pre-Roman-period hand-carved bronze-and-iron Celtic-Gaulish chieftain-and-druid surfaces under pre-Roman Gallia-Aquitania-and-Gallia-Belgica Celtic-tribal forest light. Sits at the modifier-and-cultural end of the grid, parallel to celtic and roman 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.