Serene Sigil Sky

Latin serēnus, clear / unclouded. As a color modifier, serene implies a clear-and-untroubled quality where the hue carries the visual register of cloudless-bright-day atmospheric stability. Sits at the crisp-and-calm end of the grid, parallel to placid and untroubled in usage.

Latin sigillum, little-sign-or-seal. As a color modifier, sigil implies a magical-seal-and-grimoire-symbol quality, the visual register of medieval-grimoire-and-Solomonic-sigil hand-magical-seal-and-grimoire-symbol medieval-grimoire-and-Solomonic-sigil-and-Renaissance-occult sigil-and-magical-seal-and-grimoire-symbol surfaces under medieval-grimoire-and-Solomonic-sigil-and-Renaissance-occult parchment-and-vellum-and-quill grimoire-and-occult-light. Sits at the modifier-and-myth end of the grid, parallel to rune and omen 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.