Siamese kittens are born white as well, something to do with the temperature in the womb in the coat pigments not showing until they cool a bit after leaving the womb, I'm guessing it's a similar thing for the 'siamese' marked rabbits. And possibly the reason dalmation pups are born white too.
Sorry to hear about your cats though, I hope your black one is still alive. Can you go out and look for him?