Chewie has a strip of fur that's different
He has a strip of fur down the middle of his back about 4" wide that's black, and slightly wavy. This strip also seems to stand out slightly thicker than anywhere else on his body. The rest of his fur is more sable colored, and straight.
I don't know if this is just him beginning to get his adult coat (he's 14 weeks old).
He's also half husky, so perhaps that's part of it