A rookie mistake in painting faces is giving them but one, even hue. What we see in nature is different.
This handy tutorial on facial color banding comes care of concept artist / girl magnet Carlo "Chainsaw Art" Arellano.
1) After an initial rough-in, a basic palette is chosen.
2) The base color is applied under the pencil lines.
3) Banding is loosely laid in. "Cool on the jaw, reddish on the cheeks and nose and yellow on the forehead." This has to do with how close the skin is to the bone and how much blood is flowing to the tissue beneath.
4) Banding is smoothed out.
5) Further modeling -- lips receive red, cheeks and forehead recieve lighter values, irises get a local color.
6) Forehead gets yellower, eyewhites go in, more modeling around eyes/cheekbones, nose/iris/lips receive highlights. "I paid attention to the planes and edges of the face, because light behaves according to the edges described there."
In addition to Mr. Arellano's extensive work in games and film, he's also a teacher at Pasadena's Concept Design Academy. Thanks for the tut, Carlo!