'tri-coloured' originates from English, formed by the prefix 'tri-' (from Greek) plus 'coloured' (from 'colour'), where 'tri-' meant 'three' and 'colour' meant 'hue; appearance'.

'colour' came into English from Old French 'colour' (also spelled 'color'), which in turn came from Latin 'color'; the combining prefix 'tri-' comes from Greek 'treis' (three) via Latin/Old French usage into English, and these elements combined in modern English to form 'tri-coloured'.

Initially it literally meant 'having threefold colour', and over time it has retained essentially the same meaning: 'having three distinct colours'.