Long ago, starting my first teaching position and living within city limits, I got homesick for rural life and bought 3 sexed chicks. Sold as Aracauna then, but I know now that they were EEs. Louise looked just like a wheaten Ameraucana and laid a beautiful sky blue egg. The mostly black hen laid blue also, and the gold partridge laid bright green. Now-a-days it's rare for a hatchery EE to lay true blue! These girls eventually ended up with my parents, in free range paradise, and the eggs didn't change hue.
I did some research about enhancing shell color, and it seems that carotiniods in the diet will influence the depth of color of the shell (blue, green, and brown), as well as making orange yolks. The study was on blue footed boobies, so don't know if it applies to chickens. I noticed my EE's eggs were less green during the summer when grass is not available. If anyone has a 4H student looking for a chicken project, this would be a really interesting study. I'm happy with my girls and the eggs. Someday I will find another Louise!