"A Dresden doctor relates [an example] of one of his patients, whom he designates as an 'exceptionally sensitive person,' that he could not eat a certain sauce without tasting 'blue,' i.e. without experiencing a feeling of seeing a blue color. It would be possible to suggest, by way of explanation of this, that in highly sensitive people, the way to the soul is so direct and the soul itself so impressionable, that any impression of taste communicates itself immediately to the soul, and thence to the other organs of sense (in this case, the eyes). This would imply an echo or reverberation, such as occurs sometimes in musical instruments which, without being touched, sound in harmony with some other instrument struck at the moment."
And then, a few paragraphs down, this gorgeousness:
"Generally speaking, color is a power which directly influences the soul. Color is the keyboard, the eyes are the hammers, the soul is the piano with many strings. The artist is the hand which plays, touching one key or another, to cause vibrations in the soul."
—Wassily Kandinsky, Concerning the Spiritual in Art, 1914