Hughes
On colours developing by the same laws as musical harmonies
—The physical properties of light and darkness briefly considered
—If the laws are correctly gained, harmonics of tones and of colours will agree
—Quotation from a lecture by Professor W. F. Barrett on the order of sonorous and luminous wave-lengths
—Fountain of musical harmonics, E root of B; in colours yellow and ultra-violet, being tints and shades of white and black
—All harmonics of sound and colour condense into a primo springing from the fountain
—Multequivalency of tones and colours
—Wünsch's views nearly one hundred years ago
—Clerk Maxwell's, Lord Rayleigh's, and [Harmonies of Tones and Colours, Table of Contents1 - Harmonies]

The tones between the seven white notes of keyed instruments, and the tints and shades between the seven colours, cause the multequivalency of colours and of tones; consequently every colour, as every musical harmony, has the capability of ascending or descending, to and fro in circles, or advancing and retiring in musical clef. It is a curious coincidence that Wünsch, nearly one hundred years ago, believed in his discovery of the primary colours to be red, green, and violet; and in this scheme, red, answering to the note C, must necessarily be the first visible colour, followed by green and violet, but these not as primary colours, all colours in turn becoming primaries and secondaries in the development of the various harmonies. To gain facts by experiment, the colours must be exactly according to natural proportions—certain proportions producing white, and others black. In this scheme, green and red are shown to be a complementary pair, and therefore (as Clerk Maxwell has proved) red and green in right proportions would produce yellow. The same fact has been proved in Lord Rayleigh's experiments with the spectroscope. Yellow and ultra-violet, [Harmonies of Tones and Colours, On Colours as Developed by the same Laws as Musical Harmonies3, page 20]