He may have some hip issues or any other issues with being a german shepherd but they shouldn't be related to him being White. It is just a gene like you mentioned so it is not a health problem, well I mean being white isn't not the potential limp or being too skinny. Has a vet checked him out? There is also something called pano that can create growing pain in a pup.
Athena -GSD- born 12/13/12
Luna -Shepherd Mix- born 3/20/99