While other species of cat (most famously, leopards) can and do have solid black fur, as of 2014, there are no confirmed reports of black lions. One popular alleged photograph of a black lion, dating from 2012, is actually a manipulated image of an animal that is actually white.
An animal with completely black pigmentation is called melanistic. Melanism exists in eleven different feline species, but the closest thing to a true melanistic lion have been reports of lions with large black patches or extensive black manes. For example, the extinct Barbary lion was reputed to have a black mane that extended to its groin. However, Barbary lions otherwise retained the normal coloration for their species. Some lions display a darker brown coloration than the usual tawny fur and mane; in certain lights, this dark brown fur may appear black.