To me it looks like a fertile egg that is in the first stages of development. When they first start growing the yolk will look like it becomes darker, heavier and will start to look like it's flattening out. If you don't see veins in those eggs in a couple of days I would be very surprised. Plus, I have never heard of bloodrings as early as 4 days....none that are discernable by candling anyway...
This is a blood ring. Your egg looks like some of mine that are rather porous. They usually don't hatch, but I would hold onto it unless it "weeps" or smells.