I have quite a mix of breeds, some brown egg layers, and some blue. I had this happen several years ago before the blue eggers, and I thought maybe it was a 2-shelled egg, although that wasn't what it looked like to me. Even then it was a dark brown egg from one of my Marans inside a light brown shell which looked like it came from one of the others. (This is in the last pic with a whole LOT of eggs from when the girls had found a nice hiding place for them in the garage. We knew they were hiding them somewhere!) And the first 2 photos are from an egg we got today. I am pretty darn sure the blue egger did not have a brown egg inside that blue shell. It actually looks like the brown one was squeezed inside the smaller blue shell make it crack like that. It doesn't look like the blue shell could have ever been intact around the larger brown egg. A mystery for sure!