'single-colour' is a compound formed from 'single' and 'colour'. 'single' originates from Old French 'single' (from Latin 'singulus'), where 'singulus' meant 'one, separate'. 'colour' originates from Old French 'colour' (from Latin 'color'), where 'color' meant 'hue, appearance'.

'single' entered English via Old French and Middle English from Latin 'singulus', and 'colour' came into English from Old French 'colour' from Latin 'color'; the compound 'single-colour' developed in Modern English usage as a descriptive compound.

Initially each element meant 'one' and 'hue' respectively; together they have long meant 'of one colour' and this basic meaning has remained stable into modern usage.