'plum-colored' is a modern English compound made from 'plum' and 'colored'. 'Plum' is an English word ultimately from Latin 'prunum' meaning 'plum', and 'colored' is the past participle of 'color', from Old French 'colour', from Latin 'color' meaning 'hue, tint'.

'plum' came into English via Old English/Middle English forms (e.g. Old English 'plume' / Middle English 'plum') ultimately from Latin 'prunum'; 'colored' developed from Middle English 'colourid/colour(ed)' (borrowed from Old French 'colour') into Modern English 'colored/coloured'. The compound 'plum-colored' arose in modern English by combining the noun and the past participle/adjective.

Initially it referred simply to the color of the plum fruit; over time it has remained largely the same and is used descriptively for objects or clothing that have a deep purplish (often slightly reddish) hue.