I would have guessed that it was a double or triple gene combo including pastel, albino and maybe a third color mutation. I love it whatever it is, and I hope you prove it out to be something or multiple somethings that make the white so yellow. The hyper xanthism/xanthic wash is pretty crazy looking. The yellow head definitely points to a second or third gene other than t- albinism, and the normal pattern says that it isn't anything that effects pattern. It's not IMG, but very IXG. I wonder what that snake would look like if it was also homogygous VPI axanthic. It would probably be nearly all white or a very light, almost solid gray wash. Do you know what the parents were?