First is I select the face area again using the Magic Wand Tool (W) in the Flats Channel to isolate it from the rest of the image.

With the Brush Tool (B) I set it this time in Mode: Screen, adjusted the Opacity to about 20%, brush diameter down to about 80 px, and using the base color, I basically just freehand paint along the areas you see here outlined in red. Again making note that the light is coming from her front right angle, that part of her face should be more bright than the other side.

With gradual application of the brush, I ended up with something like this.

You can further add a little more depth to your image by adding small reflective light on her left cheek and along the contours of her nose, simulating that light has bounced from a reflective surface behind her or at her left.

Next installment of this I'll show you how, by using the same technique, I've managed to color the rest of her skin.

I hope this tutorial has helped you in any way to improve on your coloring skills, and remember always that EXPERIMENTATION is the KEY.

This is my way of coloring and it has benefitted me tremendously. If there are any questions, you could drop by at the forums.