Really cool and creative idea to make a game revolving around colors like that! The controls may feel a bit clunky at the moment, but I would love to see a full game develop out of this! :D
If you'd like a suggestion, I'd recommend firstly making the color selection more immediate -- the gun selecting the colors is a really cool aesthetic, but I'd make it select them either with fully dedicated keys, or complete mouse control (e.g. with a color wheel)
Secondly, having a bit of spare health like 3 hearts/hits before dying would be great! It's very easy to accidentally slip and fall onto a blob on the ground that you couldn't see and have to re-do the level from scratch haha