Perko here's a copy and paste from vmsherp genetics that explains some of the terms and may help. I find it all a bit confusing myself.
[h=2]Xanthophores[/h]These chromatophores produce red and yellow pigments known as pteridines. These may vary in color from pure yellow to pure red, as well as intermediate shades. Xanthophores possessing a predominantly red coloration are referred to as erythrophores.
Xanthophores also retain yellow to reddish pigments contained in the diet in the form of carotenoids. Carotenoid retention continues throughout life, and intensity of pigmentation varies based on the quantity and types of carotenoids contained in the diet. Additionally, the animals' genetic predisposition towards and ability to store carotenoids will affect appearance.
[h=2]Traits which affect the xanthophores:[/h]The reader is advised to remember that any trait affecting the xanthophores may also affect the erythrophores and vice versa, since the two are interrelated.
[h=3]Axanthism[/h]This genetic mutation slightly more difficult to comprehend. Red and yellow pigmentation is not synthesized by xanthophores. There is no red or yellow pigmentation present in these animals at all. Axanthic animals typically appear as black and white, with intermediate shades of gray.
However, in some axanthic specimens, yellow pigments in the form of carotenoids may be retained in the xanthophores. Additionally, certain iridophores may reflect light in such a manner as to appear yellow. Ordinarily, the iridophores are located in the same areas as the melanophores and are masked by the presence of the black pigment. This condition may cause dark areas to appear brownish, rather than a pure black. It is certain that multiple alleles are at work here, each uniquely influencing the appearance of the specimens involved.
[h=3]Hypoxanthism[/h]Yellow pigmentation is greatly reduced in the xanthophores. However, yellow pigments in the form of carotenoids may still be retained in the xanthophores. This accumulates with age and may be a major contributing factor in the overall appearance of some animals. It would be expected that red pigmentation would also be reduced in these animals. There are most likely several morphs of captive reptiles which are hypoxanthic masquerading around under other 'genetic labels'. Few herpetoculturists have access to the technology required to ascertain the exact nature of the mutations in today's collections. Fewer still would be willing to sacrifice specimens for examination! Myself included!
[h=3]Hyperxanthism[/h]Hyperxanthic animals develop intense amounts of yellow pigmentation as they grow, most likely as the result of extreme carotenoid retention. Occasionally, the extreme yellow coloration may be accentuated into an orange coloration where none would normally be present.
Additionally, they seem to have reduced amounts of red pigmentation present. This would most likely be malfunctioning of erythrophores, and perhaps this mutation would more properly be called anerythrism. Unfortunately, this term has already been applied to another mutation (see Anerythrism 'Type A'). Perhaps much of the confusion surrounding cornsnake genetics is simply the result of inappropriate naming of the earliest mutations, leading to confusion over the mechanics involved.
[h=2]Traits which affect the erythrophores:[/h][h=3]Anerythrism[/h]Red pigmentation is not synthesized by xanthophores. Yellow pigmentation in the xanthophores is still present. Additionally, yellow pigments in the form of carotenoids are still retained in the xanthophores. This accumulates with age and may be a major contributing factor in the overall appearance of some animals. Typically, anerythristic reptiles appear as black and white animals, with varying amounts of yellow present.
[h=3]Hypoerythrism[/h]Red pigmentation is greatly reduced in the xanthophores. Yellow pigmentation in the xanthophores is still present. Additionally, yellow pigments in the form of carotenoids are still retained in the xanthophores. This accumulates with age and may be a major contributing factor in the overall appearance of some animals.
[h=3]Hypererythrism[/h]The exact opposite of anerythrism, this trait causes excessive amounts of erythrophores to be present and enabled. The result is an animal with extensive red pigmentation.