"color bleeding is a caustics thing."

Nope. As stewer just pointed out, Poser doesn't do caustics, yet it does do color bleeding. Therefore, color bleeding must not be a caustic thing.

Observe:

Now if you don't perceive much red on those pawns, let me point out that your brain is filtering it out. You see the red wall, and you expect to see some of that bounced red on the nearby pawn. Your brain does automatic and area-selective white balancing in this case. You perceive the pawn as being whiter than it really is in the picture.

Instead - let's make the red wall invisible to camera, but still contribute to IDL - now what do you perceive?

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)