Rainbow!

[Tearx]

Animes.. with.. RAINBOWS.... So far I only have Mushi-shi
Episode number would be convenient ^^

[Kosmit]

The girl in Puni Puni Poemi is sliding off of a rainbow if I recall correctly. Can't remember which of the 2 episodes was it though.

[Kanti13]

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

[Enigma]

First episode of Pokemon lol?

[EkaCoralian]

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. ^_^

[Ileia]

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.

[Haunter103]

Seven of Seven is entirely rainbow themed. The whole thing.

[Tearx]

thanks everyone ;O this helps me a lot