I'm curious about this question also for the fact that I have a four month old mini and she's all black right now and both of her parents were silver. I was wondering how old they are when they change colors. I would love for her to stay black but I don't think that's possible. LOL
Its kinda hard to see the color of Tina in my picture, but she is all silver. She looks lighter when grown out but when she is groomed she has a darker silver color. Mandy is the darker gray with some silver and she also has the brindle color on her that you are talking about. Mostly around her beard and some on her legs.
He could either be a salt n pepper... or a dirty black n silver. Most schnauzers (unless they have a certain gene) will change colors - usually starts when they are fixed or as they get older. My girl Kiba was jet black as a pup. Now she has a blue/grey body with dark grey head and legs.