[From DaniDraws.com]

One of the biggest challenges a beginning painter will face is learning to paint flesh tones. The skin is highly complex, made up of varying colors and textures; if you get one thing wrong, you could end up with some pretty scary results.
Here’s a few simple tips to help you conquer this problem.
Choosing Your Colors
Beginning artists often like to paint a caucasian person using a generic peach color. However, by simply using dark and light values of the same color, the result will often look plastic and muddy.

To make a portrait effective, the viewer has to believe in it, and he will simply have a hard time doing that if the subject looks more like a Barbie doll than a human being.
Start by choosing your general light and dark colors for your skin. Don’t simply use light peach and dark peach. Choose colors that represent your light sources and scheme or your painting. Generally, I like to choose a warm yellow-orange color for my light, and a cooler red-violet for my shadow areas. I will adjust this according to the needs in my painting.


Color Rules
Next, if you simply add a few colors to the face and give it some variation, your subject will automatically begin to look more “real”.
Here’s a few general rules:


Make these effects subtle and don’t overdo it. Keep these tips in mind as general rules, but also make sure to observe your subject for any differences or adjustments.
Skin Variations
For the fairer subjects, keep your colors cooler and more pastel-like. Your keep your reds pink and rosy, and add a few cool accents to give the skin a more translucent feel.

For your general light and dark colors, use some orange and reddish browns. The general color rules will still apply, just adjust for the darker values. Use deep, rich colors as opposed to pastels.

Conclusion
You will also want to take into account such factors as the light source and color scheme. These rules will give you a good head start, and I always have them in mind no matter what style I am using. The next time you are painting a face, be sure to pay careful attention to the colors you are choosing, and give your painting some life!

-> http://danidraws.com/2007/05/14/paint-some-life-into-your-skin-tones/ <-