Well, first of all The Color Purple falls under the broadest genre of fiction. The three primary genres are poetry, drama, and fiction.
Hair color is determined by two different forms of pigment: eumelanin (which is the largest influence) and phenomelanin. Eumelanin is a black pigment, and phenomelanin is a red or yellow pigment. Hair color is determined by three factors having to do with pigments: how much pigment is present, to what degree a eumelanin or phenomelanin is present and how close together the melanin (pigment) granules are. The more eumelanin a person has, the darker his hair will be.
Skin color is determined by the amount of melanin in the skin. Melanin is a pigment produced by specialized cells called melanocytes. People with dark skin have more melanin. How much melanin your skin has is mainly a matter of your genetic makeup.