Splatoon-How to calculate areas covered by different colors?

I’m trying to make a Splatoon like effect in UE4. I tried both Decal and Render to Target methods, but my question is how can I get the areas covered by different colors so that we can judge win or lose. Is there any good idea? Thank you very much.

I asked similar question here, but no one responded.

So, in that case I’m using few collision primitives placed on image along it’s shape. And detecting is that primitives hit by my “draw” line trace.

Maybe you can place some primitives over “paint” surface with some regular distance/grid, and do similar checks…