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.
These numbers refer are codes for the colors achieved through the use of the dye in question. Specifically, the numerals refer to the light-level of the color in question. When gauging haircolor, a scale of 1 to 10 is used to represent the lightness of the color of the hair. 1 is the darkest possible color level and would be a dark, dark brown or black, while a 10 represents the lightest possible color and would be a platinum or pale yellow blonde. The exact color achieved is determined by the lightness level and base colors in the hair dye. Knowing this allows you to know that a level 3 with a red base color would probably be a rich warm color like an auburn or chestnut brown.