
It is simply a recessive colour gene. But because a lot of people(please note I have not written all or the majority, before you all jump on me)who breed white GSD's do so simply for money with no HD or blood tests & no regard for the correct temperament let alone the GSD breed standard White(most are cream/biscuit coloured)GSD's can be bred from poor quality character & temperament wise. As some one who is actively involved in GSD rescue over half of the dogs that go though our hands are white/cream/biscuit in colour & the majority of them have temperament problems
For example a 8 month white puppy found straying with a choker embedded in it's neck that had to be cut out by the vet(yes it was actually under the skin)came into rescue via the vet(the Dog warden wanted "it"pts vet wanted otherwise)is fine with people but other dogs it will attack on sight from fear an example of a "rare"white GSD getting into the wrong hands & not being socialized, in our kennels as a sole house dog because of fear aggression with other dogs again a "white "GSD, another came directly from the owners home & took 6 months to get near due to acute fear of basically anything, now placed on a very remote farm with very very experienced GSD owners who have taken other poor character GSDs & bonded with them.
If people wnat a white GSD fine but me but & it's a big but they should have the same temeperament & character as a correctly coloured GSD & of course the same HD/haemophillia testing done
Most of the "white"GSD go back to a dog called Ingersohn Errol who is behind Quadrille of Eveley & Avon Prince of Alumvale-this dog was exceptionally nervous & details of him & his offspring can be found in Nem Elliots book Modern Bloodlines, Nem told the truth Warts n all in this book