In his 1978 book titled The Cosmic Octave, Swiss mathematician and cosmologist Hans Cousto provides an interesting way to map musical tones to colors.
The idea is based on the tonal equivalence of the octave: doubling a tone’s frequency produces the same tone at a higher pitch, and vice-versa. If you double enough times a given tone, you quickly leave the range of frequencies that can be heard by a human. But if you continue doubling the frequency, for a total of 40 times, you reach the range of visible frequencies.
For instance, if you start with an A/La at 440Hz, by multiplying 40 times 440Hz by 2, you obtain 483,785,116,221,440Hz, i.e. approximately 483.78THz. Using the Spectra software, you can then obtain a visualization of this frequency. You get the following color:
While one can argue whether the tonal equivalence of the octave can be pushed that far, switching along the way from sonic waves to electromagnetical ones, since I’m not qualified to discuss this seriously, I thought it would be at least fun to apply this technique to 12 colors of the chromatic scale. Here are the results for your viewing pleasure:
| C |  |
| C#/Db |  |
| D |  |
| D#/Bb |  |
| B |  |
| F |  or  |
| F#/Gb |  |
| G |  |
| G#/Ab |  |
| A | |
| A#/Bb |  |
| B |  |