I think we're on the same page here. While the same name is applied to cells which produce red and yellow pigments, not all cells produce both. Different genes control the production of xanthin and erythrin, and although they often get shut on and off in sync with one another, they aren't always. Broadly speaking, axanthic would mean that no pigment is produced by the xanthophores. Anerythrism would be a subset of axanthism, in which only the red pigment gets turned off. Caramel Corns would be an example. It would't be surprising to learn that the pigment precursers to erythrin were cycled through the xanthin pathway, thus increasing the production of xanthin and making a yellow-tastic snake.

More rambling.

-Cole

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