Open Void Sky

Old English open, unobstructed — used as a color modifier since the eighteenth century for hues that read as airy or uncrowded. Open blue, open green: moderate saturation combined with optical spaciousness, the slight visual breath of a hue that doesn't crowd the surface it covers. Sits at the crisp-bucket center alongside clear.

Latin vocivus, empty-or-vacant. As a color modifier, void implies an empty-and-vacant-and-bottomless quality, the visual register of Yves-Klein-and-Rothko-void hand-empty-and-vacant-and-bottomless Yves-Klein-and-Rothko-and-Malevich-Black-Square voided-and-empty-and-vacant-and-bottomless surfaces under Yves-Klein-and-Rothko-and-Malevich-Black-Square monochrome-canvas-and-color-field-and-suprematist gallery-and-void-light. Sits at the modifier-and-mood end of the grid, parallel to blank and hollow 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.