Black, White, and Brown

Doctor Alex White of the oncology department, Doctor Taylor Black of pediatrics, and Robin Brown, a young nurse, were having coffee together. "Isn't it odd," the lady observed, "that our last names are White, Black, and Brown and that one of has black hair, one white hair, and one brown." "Yes!" said the person with black hair, "and notice that not one of us has hair that matches his or her name!" "You're right!" exclaimed Doctor White. If the lady's hair is not brown, what is the color of Doctor Black's hair?