The first time I tried it I sadly did not understand what my goal was. I was shooting at everything I saw, but they kept spawning. I knew I was missing something.
So I played it again today - I managed to get one purple guy, but after that only green ones spawned and I wasn't sure how to proceed.
I did have fun trying to figure out how it worked at the beginning of the game. I also like the fact that the different colours all have an individual personality, it really makes them feel "alive" somehow (and it also makes me feel bad for shooting at them accidentally, haha). Nice work!