If I turn off GC, the yellow bloom is terrible!

This is because GC tends to balance things better, and decrease the effect of clipping.

If you don't render with GC, then you see stuff like this. The parts facing away from the lights are way too dark. The parts facing the light are clipping. This is where traditional Poser users start adding fill and side lights, and end up with 10 or more lights for a simple portrait.

Wrong, wrong, wrong.

The reason for the yellow bloom is simple. In skin, of RGB, Red is brightest. As you raise the illumination, it hits the 255 limit first, and stops going up any more. But green and blue keep going up because they are not as bright as the red component in skin. The green rises to meet the clipped red, and you get yellow.

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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)