My Lab also has normally black, deep purple skin, where it is typically pink on most dogs. If it is the natural color, it is not a problem. However, if you noticed that it has changed from pink to a black shading, then you might ask a Vet about some blood work to test the thyroid.
However, I don't believe that thyroid issues cause allergy type problems?
However, I don't believe that thyroid issues cause allergy type problems?