Can an area of skin that is white due to loss of pigmentation be tattooed over?

yes. It has actually become common for African people with pigment conditions to tattoo over the areas of pigment loss, so that they regain their original color of skin. This is not something any tattooist will do, I think, since you must have a certain color for each person, but I do know there are "clinics" in which they do this. I've seen a guy who had this done, and it looked very good. When I took a good, hard look at it, I could definetly see that there were borders and that the colored skin was different from the natural skin, but I had to study it. You wouldn't notice it in an everyday situation, and it definetly looks a lot better than light spots. good luck to ya!