"Instruments to Perform Color" is an article about the history of "colour-organs" (instruments designed to display different colours on a screen depending on the pitch played)- the part I find the most interesting is the series of colour-note associations that were developed. (I found the article at [link] but I don't know if it is still posted there.)


Castel keyboard colours for his clavecin oculaire (1700s):

C: Blue
C#: Celadon
D: Green
Eb: Olive green
E: Yellow
F: Apricot
F#: Orange
G: Red
Ab: Crimson
A: Violet
Bb: Agate
B: Indigo

Rimington's keyboard colours for his Colour-Organ (1893):
C: Deep red
C#: Crimson
D: Orange-crimson
Eb: Orange
E: Yellow
F: Yellow-green
F#: Green
G: Bluish green
Ab: Blue-green
A: Indigo
Bb: Deep blue
B: Violet


In a general way it seems to be indicated that harmonic colours are the results of vibratory effects upon the eye of multiples of like measurements, thus fulfilling exactly the analogy according to which harmonious effects are produced upon the ear.
-E. R. Monteith