I found this:
Erythrism- Having red skin and scales caused by a lack of black pigments (eumelanin), which allows the red pigment (pheomelanin) to dominate the color of the appearance (Allaby, 1991). Abnormal or excessive amount of red coloring (Holmes, 1979). The occurrence of unusual amounts of redness in an individual or population as compared to the normal pattern of the species (Peters, 1964).

Erythrochromism- See erythrism.

Erythrocystic- See erythrism.

Erythrophores- Reddish-purple pigment-bearing cells (Holmes, 1979). Cells containing carotenes or yellow pigment(Bentley, 1982). Xanthophores that appear red (Bechtel, 1985).

Erythrophore- Red chromatophore (Bechtel, 1985).

Eumelanin- A form of melanin that is black or dark brown (Mattison, 1986). Black or brown melanin (Bechtel, 1985). See phaeomelanin.
on Graziani's website at http://www.grazianireptiles.com/glossary.htm

It looks like erythrophores are xanthophores that have a red or purple appearance. That doesn't get me very far, but it looks like whether or not it is xanthophores or erythrophores causing the browning of axanthics, the technical term should be hypo-xanthic, since no matter what causes it, it's some kind of xanthophore. Back to google...