I have a hen that is as close to being a rainbow as they get with out really being one. La fiesta is a blue series yellow face type 2 opiline clear flight. A true rainbow is a blue series yellow face type 2 opiline clear wing. What color cock would I have to mate her with to get true rainbow chicks? Here is a couple photos of La fiesta.
She must have some sort of greywing, full body clearwing or clearwing mutation. If she was just a YF2 opaline clearflight she would still have wing markings. She might be a spangle opaline, but she doesnt look like a spangle. Her colouring is too full to make me think grewying, so that means she is either clearwing or full body colour greywing.
That being said, she may not be clearflight pied. Its hard to tell when she has no flights. She may be split for recessive pied and have the pied head patch.
Your best bet for rainbow babies is to find her a rainbow male! A YF2 opaline clearwing blue series. Failing that, you an opaline clearwing blue, or a clearwing blue male split for opaline at the very minimum. Yellowface is preferred in the male, but the very minimum you could use to get some rainbow chicks is a clearwing blue male split for opaline.
Without having flight feathers it's not easy to tell her mutation. She is not spangle and I doubt if she's clearflight pied either. She is opaline and she could be clearwing which would mean that she is a rainbow herself. If she is a rainbow her mate would have to have genes for both opaline and clearwing for her to produce rainbow chicks