Newton speculated Harmonics in music were organized like the color spectrum in light.
"Turns out, Sir Isaic Newton, who was looking for unifying principles in the universe, not only broke light into the colors of the spectrum but also tried to apply color to the harmonic relationships in music. Newton’s spectrum of light remains – but his ideas about color and music never quite fit together, and were ultimately ignored."
"The idea that there is a link or correspondence between music and colour is a very old and very persistent one. According to McClain’s (1978) analysis, Plato linked the major second and perfect fifth to yellow and the perfect fourth to red, in an extension of the Pythagorean harmony of the spheres to encompass planets, tones and colours. Aristotle (1984) suggested a parallel between the harmony of colours and the harmony of musical intervals. Newton (1730/1952), when investigating the spectrum of light, linked the intervals tone, minor third, fourth, fifth, major sixth, minor seventh and octave to the colours red, orange, yellow, green, blue, indigo and violet."
Sir Isaac Newton reportedly associated the 7 Solfege syllables with the 7 colours of the rainbow and surmised that each color vibrated accordingly.
Thus, red has the least amount of vibration while violet vibrates the most.
C (Do) = red; D (Re) = orange; E (Mi) = yellow; F (Fa) = green; G(Sol) = blue; A (La) = indigo (blue violet); B (Si) = purple (Red violet)
research around color sound