No idea. Want a fellow researcher?Do you have any clue as to why pink would be the only color of an egg shell, visible on the inside of a shell, (from a normally blue egg layer line) or why if there are only supposed to be White or Blue shell color, with brown as a outer "paint", we could see in a bunch of medium brown eggs we cracked open today, the brown on the inside on the egg, where it should have been white?
I realize probably not. That's what I've been trying to figure out all day though. I'm thinking it might have to do with color suppressing genes(for the pink) but I have only come across one mention of that and aside from the abbreviation "pr" and that it affects this one affects the brown pigment I haven't seen anything else about it.
I think part of the problem is that few people have the same definition of a "pink" egg. Also, I'm thinking that if a hen can eat things and make her yolk yellower, the brown inside (palisade?) may be a similar thing with the shells—not genetics as much as the material the hen has to work with.