I have no idea, but I just have to say how darling she and her brother are! And to be honest, she really doesn't seem that dark at all. Out of curiosity, who is saying that she is dark? I get comments on how "big" my little guys is. He tips the scales at 5.1 lbs. Huge. I know.
I think a lot of people are either used to seeing pics of yorkies as full grown showdogs in the ring, or as tiny tiny baby pups, and get confused when they see one in the middle.