Ok, I got the idea after losing for the first time. Switching from blue to red bullets is a nice twist on difficulty since you have to plan ahead from the coming wave. 
A suggestion was to have somehow a way to show ahead the wave that was coming, similar to what Plant vs Zombies does. This would be very fun to plan before the wave even starts.

For this Jam, I think it was lacking the donuts. It's definitely a warzone. The difficulty is also a bit weird since I felt it started way too hard already.

Good concept, mate!

It was a little difficult, upgrading your stats after a round ends was a bit stressful. The concept is great though! An improvement that comes to mind is if you were able to quickly switch out colours rather than waiting for the character to completely stop before being able to do so.