Hairei did the lineart because I fail at lineart. So tjis is how I color skin! yeah.
The first step to color is to choose a base skin color (a). To make it realistic, it should be in the lighter red-yellow colors. You know what i mean :P Then make a new layer below the original (b)(i label mine to keep it organized) Then i use the Pen tool and roughly color all the skin (c).
Now I take a darker, grayer color (a) and color the shadowed parts (b) such as below the hair, under the eyes, nose and mouth, the upper neck, etc. I used the pen tool for this step.
Now I use the blending tool on the are to make the skin more natural (a). I also use the lock alpha and add some airbrushing with color 2.
Now I make the color even darker (a) and shade the most shadowy parts with the airbrush and blend tool (b). I lock alpha to make erasing edges easier. I shade parts like the upper neck, below th hair, and under the nose.
Now i have to add just a little bit of blush, this should be a redish peachy color (a. I use the airbrush tool. DO NOT OVERDO IT! It is very easy to make them look clownish.
And on to highlighting. If you shadow, you have to highlight! First get the lightening tool and turn down opacity and up the blend (a). Then find you light source (c), and lightly lightnen the areas that would show light. Such as the chest, nose, cheeks, and above the mouth and eyes(b).
Now just fix it up and erase the edge and Voila! YOU'RE DONE!! The next tutorial iis on coloring hair, feel free to check it out!