Acid Sumer Sky

Latin acidus, sour — sharing root with English acrid and acerbic. As a color modifier, acid implies a saturated-and-citric-and-zingy quality, the bright color of lemon-and-lime citrus-fruit-flesh and acid-yellow fluorescent-pigment surfaces. Sits at the bright-and-cool end of the grid, parallel to acidic and electric in usage.

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.