ORIGINAL: YHR
I am thinking of modifying this, changing the flat cardboard target to a 3D target like a cube or a tube. This would present the same target from any angle.
If you make it to resemble a day marker it will be less prone to being knocked down due to wind or from jerky movements of the tank. The day marker idea assumes you make them out of paper so hits are easily registered.
As for the paintballs, well if those red ones work well and don't jam up the guns then that'll be the winner. One camera company I spoke with said they have 10 or 12 frequencies, can't remember, but the problem is that they are not labeled which is which. I have seen some of the non infrared cameras with up to 8 though and that would work for us.