It is impossible for mus. to convey colours, but it is customary to speak of ‘colouring’ or ‘tone‐colour’ where variations of timbre or tone are prod. by different intensities of the overtones of sounds. ‘Shade’ is perhaps a more accurate term, since the differences are often those of ‘darker’ or ‘lighter’ sound. But in his tone‐poem Prometheus: The Poem of Fire, Op.60, Scriabin introduced a colour kbd. to project colours on to a screen, intended to convey the mood of the mus. The colour‐organ was used for this purpose.