I would have to say that it is a Het Axanthic at best, definitely not homozygous. Axanthic literally translate into No Xanthrophores (cells that produce yellow pigment). Although most Axanthics "brown out" when they age, I have yet to see one that has that much yellow pigmentation. Usually the brown has a reddish look to it (it still hasn't been tested wether Ball Pythons actually carry red pigment as of yet). However, some of the newer mutations definitely lead me to believe that there is some reds in Ball Pythons.

Lstly, without paperwork, there is no definitve way to detemine Axanthic lineage without breeding.