There are lots of recipes for an olive egger. Do you know his parent breeds? Can you post a pic of him?
If he's not barred, not white, he
should make sex links over the barred Rock hens.
Egg color is going to be a wild card. They're (the Rocks) regular brown eggers. He should have one brown (with dark modifiers that are pretty complex) and one blue gene. So, his offspring with a brown egger will be half brown and half green (blue plus brown equals green). Some of those green eggers may inherit the dark modifiers from him and give an olive-ish shade, some may not and you'll get various shades of green.
If you're wanting sex linked offspring, you'll need to stay with barred or cuckoo hens. Hatchery cuckoo Marans don't lay really dark eggs, but they could be an option for making nice chicks with him.
Keep some pullets from your Legbar X Marans cross. Those should be barred, and Olive eggers. Put them under your solid OE rooster next spring and you could get some nice sex link chicks. The way the genetics line up, depending on the background of the rooster, you could possibly get honest blue eggs from that next generation also, as well as some nice olive and some dark brown.
Not that I'm an enabler or anything......