I also have a black and white boxer. He is now 2yrs. old. When he turned about 1yr. old he started to show just a little brown on his shoulders.From what I was told from the breeder he is a reverse brindle. The brindle is only noticable on his shoulders, and you have to look pretty hard.He's built, plays, and smells like any other boxer I've seen or owned.As far as being purebred, I did have a problem of getting him registered as that color. They requested several pictures of him before they would register him, and at the end he was registered as black, white, and tan. Even though there is no tan to be seen on him.