Old English deorc "dark, obscure, gloomy; sad, cheerless; sinister, wicked," from Proto-Germanic *derkaz (cf. Old High German tarchanjan "to hide, conceal"). "Absence of light" especially at night is the original meaning. Application to colors is 16c. Theater slang for "closed" is from 1916.
early 13c., from dark (adj.). Figurative in the dark "ignorant" first recorded 1670s.
Closed; not in operation: Monday is a ''dark'' day at Heinz Hall (1916+ Theater)