Final answer:
The variety of hair color is influenced by eumelanin and pheomelanin, which determine the hair's darkness and red hues respectively.
Step-by-step explanation:
The large variety of hair color is influenced by the amount, size, and distribution of two types of melanin: eumelanin and pheomelanin. Eumelanin exists as black and brown pigments, and generally, if more eumelanin is present, the hair is darker. Conversely, pheomelanin provides a red pigment, and the presence of this type of melanin gives hair reddish hues. The specific balance and distribution of these melanins determine the wide range of hair colors from blonde to black, as well as red tones. Over time, melanin production can decrease, leading to gray or white hair.