there is no such thing as gray hair....

When hair grows, either it is pigmented, or it is white. The greyish appearance of hair is only in fact a kind of optical illusion, produced by the mixture of coloured hair with white hair. The French expression "pepper and salt hair" gives a good indication of what this means. It is therefore obvious that the hair appears increasingly grey as the percentage of white hairs increases. Furthermore, since hair grows from the root, it can be coloured and yet have a white base.
As can be clearly seen when hair continues to grow after having been coloured.
The hair whitening is called canities. It is a very complex phenomenon, easily explained in the first instance - for as soon as a hair is no longer pigmented at its conception, it grows white. This is all very well, but why is it no longer pigmented? It was long believed to be the natural consequence of a halt in the production of melanin by the melanocytes. Until researchers made the amazing discovery than although the papilla producing a white hair contained melanocytes incapable of producing coloured pigments, there were others that were working perfectly, but were no longer able to transmit their melanin to the keratinocytes. For the moment, the reasons for this interruption of communication between melanocytes and keratinocytes remains obscure.

It was subsequently discovered that melanocytes were not only to be found at the bottom of the dermal papilla, but also in a reservoir situated higher in the external epithelial sheath. These melanocytes are dormant and produce no pigments. Some of these are recruited by the hair follicle to repopulate its lower part when it begins to regenerate itself at the end of the telogen phase. Once they have been selected, these melanocytes are reactivated and the production of melanin begins once more. But this reservoir is still to be found in white hair follicles. Which leads us to think that canities may be the result of a "recruitment deficit" in this reservoir. Once again, the processes involved remain a mystery.