I have a Buff Orpington that finally started laying and lays X-Large dark brown eggs...not like Marans dark, but dark...
I also noticed that higher protein gives me much larger eggs..the medium went to large, and the large became X-large, and the X-large became Jumbo when all the chickens started eating the chick starter that I was putting up there for a few younger birds...so now when I run out of laying pellets I will be switching everyone to a grower or maintenance feed with oyster shell on the side. I mean the difference in the eggs, and the chickens is remarkable to say the least. I guess that is the difference between 16% and 20% protein.