Frank Sumer Sky

From the Old French franc, free, sincere — used as a color modifier since the seventeenth century for hues that read as direct and unhedged. Frank red, frank brown: moderate-to-high saturation combined with optical directness. Sits at the crisp-bucket alongside direct and honest.

Akkadian Šumeru, Sumer. As a color modifier, sumer implies an ancient-Mesopotamian-and-cuneiform quality, the visual register of Sumerian-Ur-and-Uruk hand-built ziggurat-and-cuneiform-tablet bronze-age Mesopotamian city-state surfaces under Sumerian-Mesopotamian Ur-and-Uruk bronze-age city-state sun-baked-mud-brick light. Sits at the modifier-and-cultural end of the grid, parallel to akkad and median 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.