Here's the basic idea of how my shaders work. I use a specular node with a very broad roughness effect to figure out where there is skin facing the light, or more specifically where the reflection angle is right to see the light most strongly on the skin.

I drive that into a blender. The blender has two colors to stain the color map. The first color is for the areas in shadow - this should be a very weak brown or orange. The second color is for the areas in light - this should be a very pale blue. You'll have to play with the colors based on your color map and your lights. Once it is set up, you can usually forget it, even if you move or change your lights.

Of course there is more to it. You really want to use a Blinn specular but I'm going really basic here. Practice getting the overall skin tone right without specular, then add it at the end.

---

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)