Black (along with red) is a very old variety, tracing its history all the way to Mr. Maxey. I sometimes have waiting lists for this variety.
Black is the only variety of show mouse which must be the same color all over--ears, eyes, nose, toes, tail, etc., must all be a solid, dense, black.
Interestingly, when (well-bred) black mice are born, they're already black so they're never really "pinkies."