I did a random candle sampling last night of my eggs. I saw clear veins in a couple, dark sections in others, and one that was clearly cracked. The four celadon eggs look pretty clear, but I'm going to see how they look on Friday. My home eggs look pretty clear too, but I won't be surprised if they're not fertile since they're from the first week that one of my hens was laying.
Edit: This means that I'm down to 36 eggs in the incubator since I tossed the cracked one. It was a perfectly straight crack all the way around the egg like a plastic easter egg.