Eggs come in 2 base colors. White or Blue. There are stories of pink, but the jury is still out on that.
Brown eggs are actually an outer coating some breeds put on the shell. If you look at a cracked brown egg, the shell is actually a white shell.
This colored coating can come in various shades, from a very light, almost cream to a dark chocolate. Sometimes just the right amount can seem "rosey".
Blue eggs as well come in many shades.
When the brown coating is applied to blue eggs, usually you'll get some shade of "green". However, with the many shades of blue and brown...other colors are possible. A reddish tinted brown on a heavily blue egg can look almost purple. Usually though as the chicken lays more, both the egg color and coating tend to lighten and your purple gets more green.
Is My chicken an Ameraucana? Officially the answer is "If it does not meet the Ameraucana Breed Standard, it is not an Ameraucana." Part if that standard is color, if it's not a standard color, it's not an Ameraucana.
I would personally add..." unless it's an accepted project color " Even Ameraucan Breeders have no qualm with calling a Lavendar an Ameraucana.
As for the combs, with the mixed genetics of EE's, unless you know what the parents genetics are, you can get a lot of different combs!!
What color Orps are you putting with that Lavender Ameraucana?
My orpingtons are Blue,Splash, Lavender and Jubilee