I love the idea, and the option to change the paint color is a nice touch! that's a shame that you didn't commit fully to your concept though? like the enemies: why a snake? it would've made sense for it to be representation of the part of our mind that is telling us we aren't good enough, or just unsupportive family members of the ghost, why not? same for the tools: why a gun? why a bomb? those are war/army/crime related. could've been fun to see a spray paint can or a paint bucket? also if you really wanted a gun, why not a paint gun design inspired by those of splatoon?
Lastly, if the game want us to start painting, I find it a bit odd that it is so focused on the killing enemies part, that we lose "health" when we effectively paint the canvas. But since it make sense paint is a finite resource , a simple change of the end message would fix that, like "Even in face of the adversity you managed to finish your painting!" or something like that?
Anyway, I may be a bit perplex regarding the aesthetic choices you made, the gameplay was pretty fun and as I said, I was totally sold on the concept! well done!