That's a cool use of music! The sensation the game gives just by painting the world around is great.
However I would point this one issue: the paint gauge kinda goes against the musical idea. Having limited munitions forces the player to shoot with parsimony. Thus, most of the time I wasn't hearing more than 1 sec of the "techno-color music". Although it's more fun to keep holding the shoot button, that's not a strategy that works.
Still, good mechanic, and great execution. There's even a story, that's rare to see in a jam!