suppose I have two skin textures. What's the best way of matching one skin tone to the other?

Are you talking about piecing together parts of two different textures and making the two match? I haven't dealt with precisely that problem, but I have done something similar when compositing photos that should match in color, scale, etc. What I do is make sure the edge of the image I'm matching to the main image overlaps substantially. Then I go into each of the color channels, usually red, green, and blue, and do whatever dodging and burning is necessary to make a smooth match on that channel. When the channels all match, the composite colors will match. Finally, I create a layer mask on the image I'm matching and use an airbrush tool at low opacity, about 5 to 10%, to feather the edge of the image so the transition from one image to the other is indistinguishable. I learned to do this because I needed to digitally composite aerial photographs. It works, I've done a lot of it.

Hello, This may or may not be helpful. Go to the Cover Girl one.
Ruku
Serpent