One of my Khaki Campbells laid an egg with a blue-green spot in the yolk. They only just started laying again a few weeks ago, we washed and refrigerated. It was laid in February. Has mold set in already?
Sometimes in eggs there is a spot called a meat spot. It’s not inedible. You can eat it and be just fine. I’m not sure if they could be blue green tho.
Did you take pic of the blue-green spot? Duck egg yolks change color when they are fertile? @WVduckchick
Other than blood spots or normal occasional meat spots, I've never seen any other color inside my duck eggs.
I have Welsh Harlequin, Cayuga, and Blue and Black Swedish. I get fertile eggs from all of them, and a few times a year I get colored fertile spots from the Swedish. I'll defiantly post if I get another one!