Gray tissue in duck eggs?

[seachainanmadra]

I have a young black Swedish duck that began laying eggs about two months ago. I'm getting so many duck eggs that I'm not able to use them all, so I can't pinpoint exactly when this started, but I've recently begun finding gray tissue in her eggs. It's the little band of tissue that binds the yolk to the membrane, and sometimes the gray is darker or larger than others. All of her eggs from the past month or so have this (though I don't think the very early ones she laid did), and all of my other duck eggs have white bands of tissue. All of my duck eggs are fertile, although I doubt that makes a difference. Also, this duck does lay eggs with more bloom, and her first egg was gray, like a lighter Cayuga egg, though again, I doubt that's related.

Do I have a problem, and are these eggs safe to eat or hatch? I really want to start selling eggs, but won't until I know what's going on here.

Here is a photo showing the grey tissue.