With the german shepherd breed you can pretty much tell when they are. A GSD puppy is the same color as he is going to be as an adult.
A good white GSD should have both dark eyes and a black nose and lips. In order to get a white coat color in the German Shepherd, both parents must carry the white gene (they must either be white dogs themselves or be carriers of the white gene). The order of dominance is as follows: Melanin is produced.