I remember I learned something I was surprised with... In fact, there is only one skin tone, whoever we are talking about. That colour is yellow. Depending of the people, that yellow colour is more or less dark or light. And what makes the skin more pale is either the veins, containing blue oxygen-less blood (cutting one and the blood becomes red again, since there's oxygen in air), or lightning. As a black guy, I admit we look pale or grey-ish in winter, or with cold colour settings. But when it's summer, the warm colour of that very dark yellow shines better.
How is this related to modeling, I don't know... I need some sleep.
By the way, I like to see you progress. Because I know I will see better pictures the more time goes on.