Which part of the hair is responsible for its color?

The part of the hair that is responsible for its color is melanin. This pigment is produced in the hair follicles and comes in various types, primarily eumelanin (which is dark) and pheomelanin (which is lighter, producing yellow and red hues). The amount and type of melanin present in the hair determine its overall color.

While keratin is a key structural protein that makes up the hair shaft, it does not influence color. The cuticle is the outermost layer of the hair, providing protection but not affecting pigmentation. The cortex, which is the middle layer, contains the majority of the hair's mass and its melanin. While the cortex is crucial for the overall structure and strength of the hair, the specific role of coloring is attributed to the melanin contained within it. Therefore, melanin is the primary determinant of hair color, making it the correct choice.