From what I herd there were some. That when put next to an Ivory producing YB. You couldnt tell them apart. I herd when YB's came about There was some that were going around. People saying they were proven Ivory producers. But they were not. They were YB's if you went by the looks of them. I think thats why everyone that has any YB's for sale. They almost always say from a proven Ivory line or whatever. My YB male doesn't have alot of yellow on his belly. But his fathers belly is just crazy the most yellow I have seen on a YB's belly. Mine has a faint yellow tint with some darker yellow specks here and there on the belly. I was told when choosing a YB you look for the flames then look at the belly. Also look for the light spot on top of the head. Ive also been told just cause it looks like a YB doesnt mean its a YB. Or Het Ivory. Like said if your worried about it make sure you buy from a well known breeder. That is working with a proven line.