Unique game IMO, loved teh scenario explanation of it too to set up some background.
I did find it to be fun! However it could be more challenging, which would also make it even more fun to people like me.
I found that keeping extra enemies of all colors on screen that were already damaged is a good way to maintain low gas levels, but I feel like there should be a relation between the numbers of enemy on screen and the gas levels, since it seemed too easy to just run from them and kill one of one color and not worry about that color anymore.
Anyway I actually love the concept and had fun. Nice work!