'one-colour' originates from Modern English as a compound of 'one' and 'colour', where 'one' ultimately comes from Old English 'ān' meaning 'single' and 'colour' comes from Old French 'colour' (from Latin 'color') meaning 'hue, appearance'.

'one-colour' was formed in Modern English by compounding 'one' (Old English 'ān') with 'colour' (from Old French 'colour' < Latin 'color'); the two elements retained their basic meanings and were joined to describe something of a single hue.

Initially a literal compound meaning 'one + colour' (a single hue); over time it has been used descriptively to mean 'monochrome' and, less commonly, as a noun for a single hue or a single-colour scheme.