There's no reason a brindle and a fawn couldn't produce a white puppy, I'm sure it happens quite regularly. If you do a web search for Boxerhaven Boxers, under their Information and Opinions section there is a presentation on the genetics of white Boxers that should be helpful to you.
Again, the infraction is for breeding a dog that has a disqualifying fault, *not* for breeding a dog that has a chance of producing a disqualifying fault. If that were the case, the dogs that have a chance of producing a disqualifying fault would not be allowed to shown, either, since they would not be breeding stock and the purpose of a dog show is to evaluate breeding stock.
And yes, I realize that Boxers were around before Frau Stockmann got so involved; however she is widely credited with the preservation of the breed through the war, and you would be hard-pressed to find a Boxer in North America today (or, probably, much of the world) that does not trace back to her Von Dom kennels.
A revision simply means a change. Adding to or "shaping" the standard would be a change and thus, a revision.
I'm glad you're happy with your breeder. I'm still not sure where you get that I was putting her down, but that's really not my problem.