Yeah it's melanism, there have been a few melanistic deer (I read some place in Texas has a lot of them). The only melanistic animals I've seen in the wild in person are the longnose gar that live in our river...every once in a while there's a black one swimming around. Haven't caught one yet...the line always goes astray after multiple tries and then the fish is gone
As for albinos I've seen 2 whitetails in person this year.