off-color adj.

by c. 1200 as an emphatic form of Old English of (see of), employed in the adverbial use of that word. The prepositional meaning "away from" and the adjectival sense of "farther" were not firmly fixed in this variant until 17c., but once they were they left the original of with the transferred and weakened senses of the word. Meaning "not working" is from 1861.

Off the cuff "extemporaneously, without preparation" (1938) is from the notion of speaking from notes written in haste on one's shirt cuffs. In reference to clothing, off the rack (adj.) "not tailored, not made to individual requirements, ready-made" is by 1963, on the notion of buying it from the rack of a clothing store; off the record "not to be publicly disclosed" is from 1933; off the wall "crazy" is 1968, probably from the notion of a lunatic "bouncing off the walls" or else in reference to carom shots in squash, handball, etc.

early 13c., "skin color, complexion," from Anglo-French culur, coulour, Old French color "color, complexion, appearance" (Modern French couleur), from Latin color "color of the skin; color in general, hue; appearance," from Old Latin colos, originally "a covering" (akin to celare "to hide, conceal"), from PIE root *kel- (1) "to cover, conceal, save." Old English words for "color" were hiw ("hue"), bleo. For sense evolution, compare Sanskrit varnah "covering, color," which is related to vrnoti "covers," and also see chroma.

Colour was the usual English spelling from 14c., from Anglo-French. Classical correction made color an alternative from 15c., and that spelling became established in the U.S. (see -or). 

Meaning "a hue or tint, a visible color, the color of something" is from c. 1300. As "color as an inherent property of matter, that quality of a thing or appearance which is perceived by the eye alone," from late 14c. From early 14c. as "a coloring matter, pigment, dye." From mid-14c. as "kind, sort, variety, description." From late 14c. in figurative sense of "stylistic device, embellishment. From c. 1300 as "a reason or argument advanced by way of justifying, explaining, or excusing an action," hence "specious reason or argument, that which hides the real character of something" (late 14c.).

From c. 1300 as "distinctive mark of identification" (as of a badge or insignia or livery, later of a prize-fighter, horse-rider, etc.), originally in reference to a coat of arms. Hence figurative sense as in show one's (true) colors "reveal one's opinions or intentions;" compare colors.

In reference to "the hue of the darker (as distinguished from the 'white') varieties of mankind" [OED], attested from 1792, in people of colour, in translations from French in reference to the French colony of Saint-Domingue (modern Haiti) and there meaning "mulattoes."

In reference to musical tone from 1590s. Color-scheme is from 1860. Color-coded is by 1943, in reference to wiring in radios and military aircraft. Color-line in reference to social and legal discrimination by race in the U.S. is from 1875, originally referring to Southern whites voting in unity and taking back control of state governments during Reconstruction (it had been called white line about a year earlier, and with more accuracy).

see off-color.