I had a student who sees colors when listening to music to place small
speakers under each forearm and listen to his favorite song.
The reason was to discover if the interacting wavelets of stimulation would
increase the color experience. The idea was suggested by the Correlational
Opponent Processing model at http://turn.to/ai
The experience created in the student interesting outcomes. The ability to
see colors was significantly reduced when listening to music. The colors
were grayish and mild. The student reported a rather strong feeling of well
being and mild pleasure.