Using SVG for additive color mixing (additive blending)

Question

Coming from a graphic design background I know how to cheat to create an effect of additive color. The same basic solution is proposed in another post on here.

The p

Answer 1

This version replaces an earlier version that wasn't truly cross-browser. I realized that I didn't need separate shapes for the various circles, I could clone, reposition and recolor the original shape within the filter.