Easter eggers are generally a blue egg layer x a brown egg layer, thus laying green eggs, though they can still lay brown, or possibly pinkish eggs. Olive eggers are a green layer x brown layer thus laying an olive egg. You can make the eggs a darker olive by doing the brown as a maran or wellie that lay a dark brown egg. As to rainbow layers....that's just saying we don't know what they will lay...but it can be any color that normally occurs in chickens. I'd say it's too small 4x4=16/6=2.6666 so less than 3 sq ft per bird. While yes, they will have a run and free range time, think about winter, when they (or you) may not want to go out. Basically...you're asking them to be on top of each other. Minimum size you want to have is 4x6....but I'd probably go with 8x8 just to be sure. Also remember, anything in the coop subtracts from the available sq footage for chickens, so your nest box, waterers, feeders, grit, calcium, etc all take up floor space. Plus...I try not to count space below roosts..nothing worse than 1 chicken on the ground...getting pooped on by one above it.