Panther's black color is caused by special mutations in animal genes known as melanism. Such a mutation is quite common among the predatory members of the cat family, for example, in Malaysia, about half of all the leopards there are black in color due to melanism and are essentially black panthers.
The black color of these animals often has practical significance (since nature is always wise in its actions), so much black panther lives in dense forests, where, with a lack of lighting, dark animals are less noticeable, which makes their lives very easy.