Yep, they can look like anything. They can be barred (or I guess cuckoo) if a cuckoo marans is used to make them. Look at easter eggers, the olive eggers will look pretty much the same.
My EEXWelsummer chicks have turned out various shades of yellow/brown with dark chipmunck stripes. My EEXCuckoo Marans have all came out black with white wing tips and yellow tummies. Some look like they may have barring as they grow older. They are just chicks right now but in a few months if you want pics let me know lol. This is my first time with this cross and I'm excited for a variety of dark green eggs.
I have at least one olive egger in my group. And as mentioned, they are a mixed breed so you really don't know what they are gonna look like. But here is my Dora (when she was about 5 months old) and her olive egg (small, because she just started laying, between a leghorn and RIR).