They are called melanistic because of the excessive amount of melanin. Thus the black color. Supposedly, they are less common than albino deer which have a total lack of pigment.
When I was a kid, back around 1975 +-, there was a pair of deer on a local farm that we called salt and pepper. There was a white deer and a black deer that always ran together. They were the same size but I don't know that they were related. They eventually disappeared and I never heard of anyone shooting them. They were there for several years that I can remember.
Here is a link to a photo from the bowhunting board.
http://forum.hunting.net/asppg/tm.as...2Cdeer򱴷
Greg