Does anyone know if it's normal for a fertile khaki campbell egg to turn gray towards the end of incubation? The last couple of days, it has gotten so dark. It looks so odd next the newly placed eggs in the incubator. I can't see inside it minus the air space, so I'm hoping it's full of happy, healthy baby duckling. Does anyone have any experience with eggs turning colors like this?
Thanks in advance!

Thanks in advance!