Yes, black american bulldogs do exist, no they are not the correct color for an American Bulldog.  If you like black and want black go for it but if you want a correct american buldog to breed and show you are much better off getting an american bulldog that is white with patches of brindle, red or fawn or a dog with a brindle, red or fawn body suit.

We do not breed black ones, we are traditionalists. 

Below is a gorgeous example , his name is Venn’s Gaucho and I have included a link to the Pedigree Database website, if you would like to check out his pedigree.

Venn’s Gaucho on Pedigree Database