Well, let me say that the puppy is just too freaking cute. And being a boxer lover myself..let me just say a couple of things....
First...it would not surprise me one bit to find that this puppy is not actually part of the litter that you saw him with. He is bigger and more defined than most boxers at that age. I don't know about mixed, he looks pretty much boxer to me....of course it's always possible he had a different sire...one that was mixed himself, or just bigger than the others. Many momma dogs accept pups(kittens, rabbits..) that are not their own.
Secondly, for anyone who really wants to know more about the boxer, you can check out any of the boxer forums on line.
Here's one about the colors..
Boxer Forums • View topic - Difference in the Colors of a Boxer Coat
For such a young poster, I'm a little shocked at her avatar pic, and the signature.:yikes: Just MO
But, I know argueing with parents is like well, running into a brick wall....might have found it easier to say OH YES, we must get one this young..LOL. reverse physc.