I just found a resource called Avian Resources that shows most of the green cheek mutations with descriptions of how the genetics for each work (dominant, recessive, sex linked, etc). I didn't know that aviculture had been making so many mutations and combinations of mutations in green cheeks! They come in so many colors now, like budgies and cockatiels. This must be fairly recent like over the last 30 years. Apparently green cheeks are prolific, easy breeders in captivity because they would need to be in order to develop so many mutations and combos so quickly. I suspect the price of green cheeks will someday be on par with well bred hand raised cockatiels ($300-$500 depending on mutation). I'm not sure it's a good thing to make them so affordable because more people who aren't serious enough about giving a pet bird what it needs will make impulse purchases or buy them for children that really shouldn't have pet birds like people do with budgies. So many poor budgies are so abused and neglected! Budgies are parrots too but people treat them like decorations. So sad because they are such wonderful complex little creatures.