To begin with, 7 SRM is darker than most hefeweizens, IMO. Your recipe is probably a darker-than-average hefe. Add to that, malt extract will make beers darker than they would otherwise be and not all the calculators have extract entered correctly, for some reason. A 100% Pilsner malt Extract 1.050 OG beer will come out ~7 SRM, IME, where the same beer with 100% Pilsner malt would be ~3 SRM. I don't have much experience with wheat DME, but I would bet that it is darker than the pilsner extract. Personally, I would expect your beer to be ~8-9 SRM, which is orange to amber in color, like a good pale ale and a bit dark for a hefeweizen, but that doesn't mean it won't taste good.