One defines complementary colours of a primary colour and a secondary colour formed by the combination of other two primary colours: green (blue+yellow), for example is complementary to red. The use of complementary colours make the colours brighter and stronger. Complementary Colour if instead, the colours are mixed, variations of gray colours are formed. The combination of complementary colours has been scientifically studied only in relatively recent times and many painters have provided proof of precise cognition regarding its value. Leonardo da Vinci, in his treatise, notes, "Colours of equal perfection are shown for major excellence in company of the correct contrasting colour…..blue and yellow, red and green, because each colour is better known against its contrast rather than a a similar colour, as dark colours against white, and light colours on dark."