There are two problems associated with breeding other colors to BEW. The first has to do with the nature of the Vienna (BEW) gene itself. It is dominant, but it takes two copies to produce a BEW. One copy of the Vienna gene, and one for normal coloration, produces what is referred to as a "Vienna Marked" (VM) rabbit. Vienna marking can be as little as a few white toes and maybe a white nose, or can look very much like the pattern on a Dutch rabbit. VM may or may not have blue eyes, or even one blue eye and one brown. Rarely, you can get what are called VC (Vienna carriers) that don't show any white at all, but which can throw VM or BEW when bred. VM are not showable in any breed.
The other problem with BEW, is that you don't know what the rest of the BEW rabbit's color genes code for. It may be an agouti, a self; it might have dilution genes - you can't tell. When you breed that to a rabbit of a certain color, you can get a lot of unexpected colors. Another problem of the BEW (which you see in the REW as well) is that there are genes that code for "white noses and toeses" or just white claws that go unrecognized in a completely white rabbit. Breed that to a colored rabbit, and you may be fighting with mismatched claws for generations.
also messes with eye color. REW can look REW but eye color will have a lavender tint. not a good idea to mess with the Vienna gene. also as a responsible breeder you would have to acknowledge all offspring are potential carriers and how do you control others to do the same. having that problem now with a line. found out there is BEW in the background and i was not informed messed up my whole breeding in that one line. now what to do with the offspring..hmmm...