Here is the demo. Two big spheres, two small spheres. Each has a skin tone in diffuse color. Each has a white Blinn node for specular. On the left, the subtraction is not done, on the right it is.

Notice the yellow ring around the highlight on the left?

To connect AO, add a Math:Mul node. Connect it to Diffuse_Value. Connect AO and the 1 - specular to the Mul node.

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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)