Some hair follicles are black because the melanin produced in the follicle can cause pigmentation of the surrounding epidermal cells, as stated by the National Center for Biotechnology Information. These follicles are denser and contain higher concentrations of melanocytes as compared to brown, red and blonde hair follicles.
Melanin, produced by melanocytes, is responsible for the pigmentation of hair, eyes and skin. The pigmentation seen in the hair follicle is determined by genetic makeup and the interactions between the production of melanin, transfer of the molecules and formation of the hair shafts, notes NCBI. During this time the hair follicles are actively pigmented and the density of the melanin deposits result in varying colors.