Let's look at other portrait painters and their use of COLOR and VALUE
Sargent, and American 19th & early 20th century painter, is a great source for his use of brush strokes and rich flesh tones. See more of his work here...
Od Nerdrum is another artist, who mimics Rembrant. His work is strange, yet BEAUTIFULLY painted!
See him here...
How about Margaret Bowland? Amazing control and emotion! See her here!
How about Caravagio? the Italian master!
And others? soooo many to see check out this portrait site too!