Hairprint restores the natural pigment to your hair. Your hair has a unique genetic structure, which we call your "hairprint". It is as unique to you as your fingerprint. This structure determines how pigment is arranged in the hair, and that arrangement determines how light refracts, and refraction determines how we perceive color. Dyes do not do this. That is why hair colored with natural pigment will always look different and better than hair that is dyed.
During a Hairprint treatment, new eumelanin is synthesized within the cortex of the hair. This process is called melanogenesis and happens continuously within the body.