2 of the Fullmetal Alchemist OPs have rainbows. The second one and I think the other is the fourth.
The FMA Movie also has one.
Spoiler :
The first scene that you see Al with a human body back in their regular world. He's in the desert and he makes water come out of the ground and there's a big rainbow
Last edited by Kanti13 on Sat Dec 26, 2009 3:56 pm, edited 1 time in total.
At the very end of the Eureka seveN movie (Eureka seveN: Pocket Full of Rainbows), the two main characters are observing two large rainbows. That might work. ^_^
The second opening from Full Metal Alchemist has a rainbow in it near the end. I haven't seen it in awhile so I don't remember when they started using that opening. If I had to guess, I'd say episode 14.