Jake,
I believe that Axanthics brown out due to the presence of small amounts of eurythriphores (sp?)(red pigment), and not actually from the xanthrophores. Although we haven't truly seen an Anerythristic Ball Python yet, I believe that there are red pigments at work in these animals.

At this point, it is just a bunch of opinions, but I do always like these types of discussions. Thanks for making me put my thinking cap on for awhile.