What happens when there is an excess of melanin in hair?

When there is an excess of melanin in hair, it results in dark hair. Melanin is the pigment responsible for the color of hair, skin, and eyes. The more melanin present in the hair follicles, the darker the hair will be, leading to richer shades such as black or dark brown. This abundance of melanin contributes to the overall hue and depth of the hair's color.

In contrast, gray hair occurs when melanin production decreases, leading to a loss of color. Brittle hair relates more to hair health and structural integrity rather than pigmentation levels. Thinning hair is typically associated with factors like age, genetics, or health issues, rather than the amount of melanin present. Therefore, the presence of excess melanin directly affects hair color, making dark hair the correct answer in this context.