The Colour in Art - The Rules of Harmony: A short documentary made in 1965

Harmony is a term borrowed from the sister Art of Music to denote a degree of relation or congruity between two or more colours to mutually support or develop each other's beauties, as is the case with a chord or concord of sounds. The degrees of relation, or qualification for harmony, of sounds can be ascertained by mathematical calculations incapable of erroneous results.

Not so, those of Colours, at least in the present state of the science of Optics. If it should be proved that colours are the effect of air vibrations or any other fluid, as are sounds, the Harmony of Colours may equally become the subject of mathematical calculation, with equally certain results.

The theory of the three or seven colours being all equally necessary to each other, which has been derived from the division of the ray of light by a prism, has been supposed to afford the relative proportions of the various tints necessary to Harmony in a picture because existing in the light; and fanciful, but entirely unfounded, analogies have been drawn by enthusiasts between the seven colours and the seven notes, and the three colours and the notes of the common chord in music:

But without going into the question of how far this would be likely to assist in our present enquiry, if true, it may be sufficient to observe that these relative proportions vary with the substance of the prism by means of which the ray of light is divided; so that the whole induction falls to the ground.