The natural color of hairs is black due to presence of a dark pigment melanin. The black color is dominant over red hairs. The black hair can be pure black or hybrid black.A cross of pure black and red hair will give rise to black hair individuals. If impure black is crossed with red hair, then the probability of black and red both is present.
Red hair is recessive. Two of my grandchildren have red hair, their parents do not and were told by the doctors at the hospital that it is recessive and therefore they are both carriers.