Like steering a car with your feet (possible but may produce unexpected results) it is possible to use gray chips for controlling light intensity, but I use the intensity parameter to control intensity and leave my chips white.

Color chips that are not white or black are altered by gamma setting. If you do not firmly understand what RGB 170, 170, 170 really means with and without GC, and you're experimenting with gamma as an artistic control, you may be changing more than you mean to.

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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)