Now that you have your skin all selected, and your in CMYK mode (you are in CMYK mode right?), it's time to color.Make sure your original layer is selected (it should be the only layer right now) and your skin selection (from page 3) is still up, and go up to Layer -> New Adjustment Layer -> CurvesName the Adjustment Layer "Skin" and click "group with previous"This will bring up the curves dialog box, and it will add a layer to your layers palette:This is where all the magic happens. As I mentioned before, since this is an adjustment layer, you can always go back and edit it by simply double clicking on the curves icon in your layer palette. The black and white image to the left of the curves icon is your mask layer, which can also be edited (if you need to reveal more or less skin for some reason).By adjusting each color curve individually, you will add color to your selected area. Now you can memorize exactly which values of curves give you what color, or you can just play around and eyeball it (what I do). Raising the curve up and to the left gives you more of a color, and down and to the right less. You can also add points to the curves, and tweak the highlight and darks to be different hues, but for now I'll just keep it simple, with one point curves.This is what my curves looked like after messing around and eyeballing the skin tone:You can also adjust the Black levels the same way if you want your shadows to be darker, and the combined CMYK curve will adjust the brightness and darkness of the entire range.Click OK, and your image should look like this: