Depends on the scene it's being shot for. A rainbow could absolutely fuck up the mood you're going for. The sky in big budget movies is almost always changed in post anyway now because cg sky is easy and holding up production for a rainbow is expensive. I'd be more concerned about burning daylight to wait out a rainbow that can be fixed later. I'm pretty familiar with The Odyssey and can guess the broad strokes Nolan is gonna paint with cause he's Nolan, I'm gonna guess a rainbow in the background would be really distracting