The Rainbow is a new breed from the hatchery here in Iowa. They are supposed to be a dual purpose bird with unique, colorful feather patterns. So far I am pleased with them. They seem to be a fairly calm bird and some of them do have lovely feather patterns. Time will tell.
I've seen them, but never had any. They are also sold by some hatcheries under the names Dixie Rainbows and Pioneers. They're suppose to grow faster and get larger than the Red Ranger hybirds. Good luck with your Rainbows.