By the way, this is all good material in preparation for understanding the Diffuse node. If you have a firm grasp of color arithmetic, i.e. what does +, -, *, and / mean for colors, then you'll be able to follow so much better.

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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)