something about colour and music:
Voltaire, a friend of Castel’s, claimed that Kircher was also the source for Sir Isaac Newton’s analogy between the seven bands of color in the spectrum and the musical scale; Newton had supposed that “colour may be distinguished into its principal degrees, red, orange, yellow, green, blue, indigo and deep violet on the same ground that sound with an eighth is graduated into tones.” Castel took Newton’s spectrum as the basis for his color keyboard, but he developed twelve mid-tones for corresponding semi-tones: B was blue; C sharp, celadon (blue-green); D, green, and so on. The color-octave repeated a tone lighter an octave up and a tone darker an octave down. The correspondence between music and color had another interesting and even earlier precedent, which may also have inspired Castel. In the eleventh century, red or yellow lines placed above musical notation indicated the aural pitches of F sharp and C for singers.