This first can be caused by scarring of course. If it is a few isolated hairs I may suspect that.
It can be caused by normal aging.
Now, I did have an entire litter where all the chocolates looked like someone shook salt on them. This appeared at about 12-16 weeks. Oh, the scandal it caused! Imagine my poor pup owners. Some were worse than others. A couple owners bought HAIR DYE............I told them to wait it out......... we all waited and when they blew puppy coat everything was normal. 3 of those went on to produce puppies and it did not appear. I do have a great-grandbaby of one of those dogs that is exhibiting the same phenomenon in a mild form.
The info I got is that it is a natural occurance for puppies in some lines and happens in all 3 colors occassionally, resolved by 12 months of age. I got this info from breeders of chocolates for an avg. 40 years, some of them have left us.
I have had Labs and Nflds go through the "grey syndrome" I called it.
I had two litters out of the same lines (repeat breed) where, at I'd say 7 months of age, they started to grow in salt and pepper. Can't be the food since I did keep one and the rest were sold as pets. Only a few in each litter turned salt and pepper. When they shed that puppy coat, they grew the normal black coat.
Funny but I have never had it since so it had to be that certain gene pool.
The Nfld litter did the same thing, and I kept two pups that went completely grey then coats shed to bring in that normal shiny black coat.
Mystery that I never solved.