At risk of starting the old debate about Ameraucana vs Easter Egger, which can be the same thing - cross breeding of blue-egg breeds to arrive at a blue-egg laying breed that will often lay a broad range of blue, turquoise, olive green, and even tan colored eggs.
Another disclaimer: shades of color in the green to blue range are very often misidentified by people due to slight variations and degrees of human color blindness. It's very common to come upon two people strenuously arguing whether a certain color is green or blue. So it's a common thing to mistake the quality of color of EE eggs, as well as blue eggs from a pure blue egg layer.
I'm not an expert or even minimally knowledgeable of poultry genetics, but I do understand egg color. I have both Cream Legbars and EEs (hatchery called them Ameraucanas.) These breeds both start out by building a pure blue egg shell around the egg in the shell gland. This means that this color is part of the shell and will not rub off as is the case of all other colored eggs which all begin as pure white eggs in the shell gland.
In all colored egg layers except for true Ameraucanas, Araucanas and Legbars, the white egg shell has a tint laid down after the shell is formed. The tint is made from discarded red blood cells, and according to breed, the tint may be a light cream or a darker tan as Speckled Sussex lay, or a reddish brown as Welsummers lay or a dark chocolate brown as some Marans lay. The heavier the tint of red blood cells, the easier it is to rub off, by the way.
In the case of EEs, they are genetically blue egg breeds, but they have mixed genes for other colors on top of the blue. So if you have an EE with blue egg predominant genes, you will get blue eggs nearly identical to Legbars. This is how I ended up with several mixed EE and Legbar chickens since I couldn't distinguish a pure blue EE egg from my Legbar eggs.
So, if you have an EE that lays greenish eggs, she has a gene for brown eggs along with her blue egg gene. My EE Ethel starts out with a blue egg in her shell gland, but she lays down a layer of brown tint over the blue which make a greenish/olive color. Another EE Louise lays a turquoise egg. Her blue egg gets a very thin squirt of blood cell color just enough to deepen the blue with a hint of green which can be mistaken for a purer blue than a Legbar. But a slightly color blind person will believe they are seeing a purer blue. (About the only time our eyes can lie to us.)
Hope this doesn't confuse you all, but I really get excited about what makes eggs colored.
