A white boxer is not the result of any sort of genetic disorder at all. It is simply a dog that received two copies of the gene causing flash (white markings) - one from each parent. Without that gene, the dog will be predominantly solid coloured. With one copy, it is flashy. And with two copies, it is ultra-flashy (ie. white or predominantly white). That's all. No genetic "defects" or disorders in the mix at all.
Coat colour and its inheritance is a little more fully explained at www.boxerworld.com/coat_colour
As for reverse brindle, that is a term used in North America to describe a dog with an extremely high concentration of brindle striping. In some parts of Canada, the same colour is called "seal" brindle. Elsewhere in the world, it is just called dark brindle. Note that "extremely high" does not mean just a lot - and most of the dogs people describe as "reverse" brindle are not
A dog that is reverse brindle has the appearance of being black - it is only upon inspection that you will see (and should be able to clearly
see) the fawn. This is "reverse" in the sense that it appears that the dog has a black base coat, and some fawn striping. In fact, it is an extremely high concentration of black stripes on fawn ground colour - just like any other shade of brindle.
Insofar as the boxer standard goes, the colour is allowable in the US and Canada, but a fault elsewhere (just as an extremely "light" brindle would be - meaning one that is fawn with just a few faint brindle stripes).