Which type of melanin is responsible for black and brown hair colors?

Eumelanin is the type of melanin responsible for the pigmentation in black and brown hair colors. This pigment is classified into two main types: eumelanin and pheomelanin. Eumelanin comes in shades ranging from brown to black, contributing to the darker tones in hair. The more eumelanin present in an individual's hair, the darker the hair color will typically appear.

In contrast, pheomelanin is responsible for lighter shades such as blonde or red hair, which means it does not contribute to black and brown hair colors directly. Mixed melanin refers to a combination of both types, but eumelanin specifically is what gives rise to the dark hues. The term "oxidant" refers to a substance that can cause oxidation, which is not directly related to melanin or hair color. Thus, eumelanin is the correct answer, as it clearly explains the pigmentation associated with black and brown hair.