I've never seen an Ameraucana or Easter egger egg that was true, pure blue. They might exist somewhere, but even the bluest eggs from the Ameraucanas I've raised had a slight tinge of green, like a Robin's egg. And any chicken egg that is 'blue' always has that color through the whole shell and the inside. It's brown eggs that aren't brown all the way through because the brown color is added later on in the egg laying process and is only a coating, not the shell itself.
I think the best way to tell Easter eggers and Ameraucanas apart is by color. Ameraucanas only come in a few specific colors, black, blue, brown red, wheaten, blue wheaten, white, buff, and silver (plus the non-standard lavender color.) They should all have slate blue legs. If your birds aren't those specific color varieties and if they have green or yellow legs then they are sure to be Easter eggers. And Easter eggers are way more common even now.
I think the best way to tell Easter eggers and Ameraucanas apart is by color. Ameraucanas only come in a few specific colors, black, blue, brown red, wheaten, blue wheaten, white, buff, and silver (plus the non-standard lavender color.) They should all have slate blue legs. If your birds aren't those specific color varieties and if they have green or yellow legs then they are sure to be Easter eggers. And Easter eggers are way more common even now.