Well, we know that to some degree color and temperment are related simply because a lot of the genes related to the development of each are together on the same alleles. (one for melatonin production and one for oxytocin production, for example)
White GSD's and Boxers are not necessarily albino, and they don't have that "lethal white" problem like some breeds although in boxer I believe deafness becomes an increased risk. However, in my experience, both are a little "off". White boxers are quite often... for lack of a better word... f-ing nuts. (not dogs I would want to live with, but that's just me)
When I worked at kennels, every white boxer I ever met was one of the "special" dogs that had to be covered and had to have a special run so they didn't hurt themselves with their insane hyperactivity.
You can see an example of an interesting study done with the Silver Fox where animals were selectively bred for temperament only, and a total change in color was observed as generations passed. (the study was done to see if it was possible to very quickly 'domesticate' a species using selection only for temperament, it actually was quite amazing how quickly they had foxes that behaved very similar to dogs) They are called "Balyaev's Foxes" named after the researcher.