I read an article somewhere written by Becky Pelton, which covers this subject. As I recall, when she was working on the creation, she tried a black male from a blue line (silver based) over an ermine female and didn't get any ermine chicks. Then she found a male from a black line (gold based) and had success with that bird. Don't quote me on that, but that's the best I can recall. You should reach out to her for more info.