What is the difference between the blood island that forms in the egg and a red ring?

[Goodale13]

I know a red ring is a sign of a dead embryo possibly. But I read somewhere that an island forms, a circle where the veins begin to develop. Does anyone know the difference in appearances? I have a couple with rings in them, (the shells are dark to clearly see). The rings are probably the size of a pea (these a button quail eggs, mind you). I can see a shadow in there as well, but it could be just the yolk? I am very new to candling and its quite hard to tell what it is I am actually seeing. One moment I think, 'oh yes this is a bla bla bla' and the next I am like ' but it has this, so that means its dead' ...

So frustrating!!

 

[Pyxis]

The blood island is a circle that shows up on the yolk, while a blood ring is a literal ring of blood that circles the egg around the middle usually.