Each person you take for a portrait has their own color balance, if you like, and that, depending on their skin tone and their hair color and their general appearance.
The one possible application of the study could be to try to mobilize those stock stem cells to go back to the area where they get access to the signals to produce hair color.
It's normally not a natural colour, but some people are lucky enough to have naturally white-blonde or platinum hair, it's a really interesting colour.