Your meter do not know whether it is a white skin or black coal. It sees the world as medium gray. If you spot meter the skin, then you have to decide where you have to place the skin on Zone Scale. This is the same for metering the shadows...

For white skin, it is recommended to place either on Zone VI or Zone VII and where as Zone III or Zone IV for shadows. It all depends on how you visualize and what you want on the negative.