Open Irish 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.

Old English Irisc, of-Ireland. As a color modifier, irish implies a Hibernian-and-peat quality, the visual register of Irish-Hibernian hand-built peat-and-stone-and-thatched cottage-and-pasture-and-bog surfaces under Hibernian-and-West-of-Ireland peat-bog-and-cottage atmospheric light. Sits at the modifier-and-cultural end of the grid, parallel to welsh and celtic 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.