Edit: I also forgot to mention that having the key instructions on the ground was brilliant!
Nice job, there's a lot to like here with lots more potential!
I really liked the art style with the music, I think it meshed nicely together. The gameplay is simple but a satisfying loop and the idea to use the colored bombs to progress is nice. The boss battle at the end was a really cool idea especially.
Just some personal observations: I think the sfx is aggressive compared to the rest of the game and doesn't fit the vibe. Choosing some pleasant sounds when you pick up items, collide, shoot, etc. I think would go a lot way to improve the feel even more. I think the collision boxes on the boss could be a bit forgiving, and I didn't actually realize it did so much damage until I died a couple times, so possibly some more feedback on that end would be nice. I think a cool idea could be maybe flashing your character when they get hit, slowly losing color as you take more damage? Another issue I had was seeing enemies before they get to you. I think when you're moving, you should stick closer to the center of the screen (or make the camera drag faster).
Some ideas I had while playing are that I kinda like how the enemies stick to you. I don't know if this was completely intentional, but the idea of collecting this sort of "burs" as you go and slowing down the more you have is kinda neat. When I was playing, it was making me think of paint, so leaning into that might be pretty cool. For example, when you kill an enemy, they leave a splatter of their color behind? Maybe when you shoot them, it splatters their paint? Also I think to really push the theme, you could lead into the color coding. I think making every enemy like the boss, where you need to use a specific color to destroy them would be really neat. That would be a nice way of increasing difficulty as well as variety.
I really dig this one. It looks great and has great ideas. I'd love to see it developed further!