Acid Road 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.

Old English rād, journey / way. As a color modifier, road implies a paved-thoroughfare-and-traffic quality, the visual register of Roman-Watling-Street-and-Fosse-Way hand-laid Roman-paved straight-line agricultural-and-urban road-bed surfaces under English-Roman-road open-country sky. Sits at the modifier-and-place end of the grid, parallel to lane and path 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.