'three-colour' originates from Modern English as a compound of 'three' and 'colour', where 'three' comes from Old English 'þrīe' meaning '3' and 'colour' comes via Old French 'colour' from Latin 'color' meaning 'hue, appearance'.

'colour' changed from Latin 'color' into Old French 'colour' and then into Middle English 'colour', while 'three' comes from Old English 'þrīe' and developed into the modern English 'three'; the compound 'three-colour' formed in modern usage by joining these elements.

Initially it literally meant 'three + colour' (i.e., having three colours), and over time this literal descriptive meaning has remained essentially the same in modern usage.