complementary colour 
noun
A colour that combined with a given colour makes white or black.Everything you ever wanted to know about colour is here: from complementary colours, colour combinations, shades, tints and contrasts - the list goes on....
- His manner of juxtaposing primary and complementary colours anticipated French 19th-century developments.
- If you want to darken/shadow/brighten a light colour you are using, or lighten/brighten a dark colour, adding a splash of the complementary colour to the pure original colour will usually work better than adding any other colour.