I am pretty new to chickens, only having them since April '10. I recently gave away my two young roos then noticed my hens eggs were fertile (based on the doughnut or bulls eye). I've held two eggs back to incubate in my homemade incubator. Its early, I just set them on 6/29. So, today would be day 4. These are blue/green eggs. I can't stand the waiting to see if I am correct, that these eggs are truly fertile!!! Sooo, today I candled them. I see the very dark yolk but cant tell if there is a ring inside (blood island?) the yolk. When I candle the egg from the side and turn the egg, the yolk always comes to the top (like a level bubble). There is an intact air sac on the end that does not move. To compare, I took two eggs from the refrigerator and candled them, they look empty (couldn't see a yolk). At this point, does a dark yolk that shows in candling mean something is growing in there or that I am slowly cooking an egg? Thanks in advance!