Nice game, the art and music were done great! The gameplay itself is quite unique, with the player being able to deal damage to the monsters only with the correct colored bullets.
However, I don't quite see the point for why you should shoot first and then explode the bullets at correct timings. My strategy for defeating the enemies was to simply spam the space button and keep shooting at the enemies, changing colors whenever needed. I would have changed it so that there would be maybe some kind of limit to the amount of explosions you can do, and then regain those thingys with a short cooldown.
Overall though, there's not much to criticize about, and you two have done a good job of turning the theme into a pretty great and fun game!