The melanin content of the skin on your body determines the shade of skin that you see. The skin of the vaginal canal has no melanin. Neither does skin inside your mouth, on the palms of your hands and the soles of your feet. The vaginal skin takes on varying shades of pink dependent on the blood flow to the area.
The outer mucosa of the labia minora can have dark pigmentation, but the vagina itself, meaning the intercourse and birth canal, is pink. There isn't a way to add pigmentation if you don't have the black color you desire. For more information, click on the link below.All the best.