Hmm this might explain why I pluck the odd grey hair, only to find that it is only grey at the oldest end, and the newer hair is back to normal colour.
So the hair stopped being grey halfway through growing... Less stress?
This happened in my (31yo) beard, which allowed me to watch it shift grey and back in a short time, and it absolutely coincided with ~3 months of work where I was killing myself, and went away when I took 2 steps back and resumed riding my bike outside a few times a week.