A black Lab is a Labrador Retriever in the breed's original color, not a separate breed. Labs descend from the St. John's water dogs of Newfoundland, later refined in Britain as gun dogs, and they still have the otter tail, broad head and dense, water-resistant double coat made for retrieving. Some have a small white spot on the chest.
Color doesn't change personality. Black Labs are typically friendly, food-motivated and eager to please, though dogs from field lines tend to be leaner and more driven than those from show lines. Expect a dog that wants daily exercise, steady training, measured meals and regular brushing, since the coat sheds a fair amount. Most Labs stay boisterous well into adolescence before they settle.