Grey hair as a senescence detector?
Last I heard (years ago) we didn't know what caused hair to go grey, but recently on a Joe Rogan podcast (YouTube) Dr Rhonda Patrick, a person I follow as she gets in depth on longevity topics (see her FoundYourFitness channel), said that it was caused by senescent cells. This is why grey often comes in as patches of grey, because one senescent cell will 'sicken' the cells around them, as they do.
Anecdotally I found myself going a little grey in my mid/late 40's, and not too long after started my fasting regime, and what appears to have happened is that I got a bit less grey subsequently, and at least I haven't gotten any more grey (8 years later).
Anyhow don't know the truth of this and haven't done any research but thought to put it out there.