I think you can get a light olive by crossing EEs and regular brown layers - when I was growing up we had a mutt flock that started off as EEs (Murray McMurray called them Araucanas, of course; that was 20+ years ago and they didn't even use the word Ameraucanas yet) and RIRs and Barred Rocks from Hardy's Hatchery up here in Massachusetts. Within a couple of years we consistently had the kind of light olive egg that a lot of people on BYC are calling OEs (when I found that thread I thought Oh, look, the eggs I ate as a kid). You will NOT get the dark olive/gold/oak egg that comes from crossing back in to the Marans and strictly selecting. But honestly if what you have is a typical laying flock with no Marans and you like the look of the lighter olive eggs, they're certainly not out of the question. It's just a "dirty" or sooty green egg, so picking any of the genuine brown layers (not the tinted layers) will get you there.