I am using skin tones metaphorically in this deck as well. I will generally keep them in a range of natural human skin colors, so that they are not too disturbing, though.
My first thought was that the Fool should have skin the pale green color of budding leaves. But, that made him look like he was ill. So, he's just scholarly pale. Never been out in the world to get experience, and pick up a tan in the process. Yes, he's gonna get burned...