True Nadir Cerulean

Old English trēowe, faithful — used as a color modifier since the seventeenth century for hues that read as the canonical version of their family. True red, true blue: the saturation is full, the hue is neither shifted nor adulterated. Sits at the center of the bold and crisp buckets, marking the unequivocal middle of any chromatic family.

Arabic naẓīr, opposite-of-zenith. As a color modifier, nadir implies a downward-pointing-and-low-point quality, the visual register of celestial-sphere-and-downward-Nadir hand-downward-pointing-and-low-point celestial-sphere-and-downward-and-Nadir-pole nadir-and-downward-pointing-and-low-point surfaces under celestial-sphere-and-downward-and-Nadir-pole astronomical-and-celestial-mechanics downward-axis-light. Sits at the modifier-and-cosmic end of the grid, parallel to zenith and axis in usage.

From the Latin caeruleum, originally referring to dark blue paint pigment of the Roman world, then via French céruléen into English. As a modern art-supply name, cerulean blue is the cobalt-tin oxide pigment introduced in 1805. The color refers to a clean, slightly green-shifted blue with the matte finish of mineral pigment in linseed oil: lighter than cobalt, deeper than aqua, with the painter's weight of a word for sky.