i always thought that german shepherds can come in white, but i just read that they are not supposed to come in white.
is that true?

White colored GSDs are a fault and should not be bred. Yes, it is true.

Yes, they are true German Shepherds. White coloring is undesirable though. The white German Shepherd is not breed standard and cannot be used in show or breeding, but they are purebred.

AKC wise? The AKC disqualifies white dogs. It's a shame, they're so beautiful, but they're disqualified. Otherwise they have the exact same GSD traits, they're just not recognized by the AKC, which isn't a problem for me since I don't plan on showing my dogs.

http://www.akc.org/breeds/german_shepherd_dog/

Just because the color isn't in the standard doesn't make the dog NOT German Shepherds. White Boxers do not fit the standard, but they are still boxers.

Yes, white shepherds are "true" german shepherds. The white is a genetic mutation, can be very attractive, but it is not "to standard" and a white gsd cannot be shown in sanctioned matches. pets question and answers,www.5d2d.com

White trait often comes with some eye problems or deafness. We had one for nearly 18 years, beautiful dog, but very high strung and went blind in one eye even with vet treatment.
You should never breed a white gsd, but the mutation comes out sometimes with normally colored dogs, so treat them as pets and spay/neuter.

The color is simply a disqualification, meaning the dog can't be shown, but are still AKC registrable. They do come with the risk of more genetic issues, and must be bred carefully http://wsgenetics.org/breeding.htm