johnpf is right - the intermediate value is different because the subtracted color is different.

The subtracted color is arbitrary and whatever you want it to be, since the goal of this shader group is to alter the contrast around a particular color, whatever that may be. But it is a control parameter that decides how to anchor the contrast adjustment in color space. By choosing a different control color, you get a different calculation.

Even in Poser. See above image.

 

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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)