Red light mixed with green light produces yellow light. Yet, a red photon and a green photon don't combine to make a yellow photon (or two of them). Can someone explain this?
Redbelly eloquently explains it. If you did a spectrographic analysis (or simply passed it though a prism) you would see that the red and green light is still there, and that there is, in fact, no yellow light at all, except in our minds.