Yep, Kathi. It was fashionable in the early part of the twentieth century to write "psychological" music. Here are three composers who incorporated the idea of synesthesia into their music:

Alexander Scriabin
Vasilly Kandinsky
Olivier Messiaen

Scriabin composed a piecce called Prometheus, Poem of Fire. In the score for this piece is a "color organ" which was supposed to project colored light as it was played. In Scriabin's lifetime, it was never performed with a color organ, though. The technology just wasn't there. Scriabin did want his audience to see what he saw when he composed the music. The synesthesia was a big part of how and why he composed that piece.

Vasilly Kandinsky may of may not have had synesthesia...but the idea of synesthesia was incorporated in the composition of pieces meant to induce an association of color and music to his audience.

Olivier Messiaen, one of my favorite composers, was proven to have synesthesia. He developed a system of "synthetic" scales associated with different colors. Of all the claims of synesthesia, his is the most believable. He was a devout catholic...very spiritual...did not take drugs to induce the association of color and music...and he used this simply as another way to think about music. He went through numerous tests by psychologists and his synesthesia checked out consistantly and repeatedly.