Color Hair color resides in the cortex. Though keratin, the main component of hair fibers, is colorless,melanin, also found in the cortex, is responsible for characteristic hair color.
Melanin granules are formed in the melanocytes at thebase of the hair follicle (the dermal papilla), which secret emelano somes into keratinocytes.
In the anagen phase,melanosomes are transferred to cells in the cortex and the medulla,but not the cuticle.
Melanin granules are spread throughout the cortex, more densely so in its outer most part,yet do not enter the cuticle. There fore, to alter natural hair color effectively, hair cosmetics need to get beyond the cuticle into the inner part of the hair shaft.