I used to get them quite often. And the project they came from was one you would not expect these to come from.
Years ago I had in mind a project to produce pure yellow corns with black blotches on them. So I bred Butter/Caramel into my 'A' Anerythristics, figuring this would be a logical start. To make a long story short, the project was a dismal failure. And the failure was because the 'A' Anerythristics coming out of the later generations lacked all traces of yellow on the sides of the head and neck. I have since gotten rid of just about all of those animals, so I am sure they are popping up here and there in other peoples' collections by now.
Of course, this brings all kinds of odd questions to mind about what the Caramel gene is actually doing......