Haven't seen any marble or white knives in the states, other than I think oddball imported some and they might be in his photo thread in the photo lounge..
I went and tried to find the pix again, if you look in the vendor section there is a "Neo Book Store" (mfk owner) and he sells the originol MonsterFishKeeper books.. that is where the one calico pic knife was pulled..
I guarantee its from selective breeding (those asian breeders are pretty crafty) and the fact that they probably were spawning BGK with hormones 10-15 years ago.. they grow out the ones from each batch with the most dominate white stripes and re-breed them over and over to get new color morphs - just like any other 'morph' animal like leopard gecko, corn snakes, albino bichirs, etc, etc..