I'm not an expert and don't really know the answer to your question. But this is what I've noticed. I have a black poodle who has a lot of white/gray hair all through her coat. She is at least 12 yrs old, but she has had them forever. I groom a couple of other black poodles who have also grown the white/gray hair. I've been grooming one of them since she was a puppy and the older she gets the more white/gray hair appears. I'm just guessing it is the norm with these dogs.
"There is no psychiatrist in the world like a puppy licking your face."