Ignoring the horizontal lines on the face in the 1st image you posted, what he is basically doing is posterizing both the hue and the luminosity of the image. It also looks like there may also be some posterization of saturation. He may link posterization of the hue and saturation together so that he doesn't wind up with too many combinations of these two variables.
To separate out the hue, saturation and luminosity components in preparation for posting them, I suggest you use an old plugin called HSBHSL.8bf which will separate out the H, S, and B (or L) channels with one button-push. You can download it from Adobe here:
http://www.adobe.com/support/downloa...29&PID=3350462.
You can then posterize each of these 3 coordinates with a conventional "Posterize" adjustment.
This being said, the problem you are likely to run into is that a straightforward application of the above method will likely yield splotchy, irregular areas, not nice simple borders. To simplify the borders, you will need to smooth the image somewhat before you apply posterization.
However, to be honest, it might just be easier to paint in the colors you want by hand, perhaps guided by a simple, normal, but disposable posterization of the entire image to guide where you paint.
HTH,
Tom M
