The importance of colour is linked to Messiaen's synaesthesia. Wrote a Treatise of Rhythm, Colour and Birdsong. Messiaen wrote descriptions of the colours of certain chords. His descriptions range from the simple ("gold and brown") to the highly detailed ("blue-violet rocks, speckled with little grey cubes, cobalt blue, deep Prussian blue, highlighted by a bit of violet-purple, gold, red, ruby, and stars of mauve, black and white. Blue-violet is dominant.