I am adding some of the basic flesh tones in the lit areas but more contrast will be needed as it progresses. I have a W&N preprepared flesh tone but only use it to add to the whites and yellows to make a basic flesh colour of my own. When I want to deepen it I also use Burnt Umber, Alizarin Crimson and a green biased blue. The use of complementary colours in facial shadow is well known, and, in some modern portraits, exaggerated to great effect.