NERD says it's a random occurrence. I think the "faded" albinos and the "high contrast" albinos are more of a selectively bred trait, and not an actual mutation themselves. They are all just T- albinos. If it were a proven mutation, seperate from your every day albinos, you could breed a faded albino to any dark normal, and breed any of the hets together or back to the original faded albino and end up with all faded albinos every time. They wouldn't likely be compatible with your common T- albino, and the amount of xanthiphore in the breeding stock wouldn't have an effect on the faded homozygous albinos, and I don't know that to be the case.