I have limited experience with any eggs let alone brown eggs (have 2 brown egg layers) and can say that they shades of brown can be different. I've even had lighter shades on the same egg. Asked here and was told it is fine. Ate the eggs and I'm still around
Yes, 8 of my brown egg layers all lay different shades of brown, and I can tell which is which by the shade and size (some hens are older, so lay bigger eggs). The EE lays a blue/green colored egg which doesn't change much in shade. The different shades look quite pretty in the egg carton!