I'm assuming that the sponge is either absorbing or otherwise disrupting the red light in a given area. Which is a rather fun idea, but I believe the effects are wrong.
Removing red light (before or after it is reflected from a surface) won't cause red objects (or light sources) to become green. Red objects are red because they absorb other colors but reflect red light -- if the red light is gone, they will appear black. Yellow objects, however, would appear green.