Either way will produce OEs, as long as you are crossing pure breed birds. If you are breeding with a pure Ameraucana & pure Marans, then the parent birds will have two blue egg genes and white egg genes w\ dark brown egg modifiers, respectively. The offspring from this mating will get one blue egg gene from the Amer. parent and one white egg gene w\ dark brown egg modifiers from the Marans parent. This will produce an egg in a shade of olive green.
Breeding OE to OE is the crap-shoot. Because each OE would be carring one of each gene and the offspring could end up with two blue egg genes or two white egg w\ dark brown modifier genes.
Hope that isn't too confusing!
Thanks for this information it makes sense to me. I had asked a while ago if olive eggers bred together would produce olive eggers and was told yes they would. However this makes more sense to me. Thanks, Mike