WHY "UNDER THE RAINBOW" ?

Since I think that the title is one of the most important things in a fanlisting, I thought about a lot of them for Hakuren and Teito. I would dedicate something that suits them, something that could describe the "core" of their relation in a few words.

Thinking about them I found "Always for your Sake", because Teito and Hakuren become friends in the moment when Teito tells him "Now I can protect you, we are friends!".
Teito's heart is unsure and he was hurted from Mikage's loss, so he needed to become a person that can look to the future thinking of the sake of the beloved friend.

I thought that that one would suit as title, but yesterday, in a raining day I look at the sky thinking of the rainbow, and that was the moment when I thought about a legend that says that under the rainbow there's a treasure.
And an Italian saying (I really don't know if in the rest of the world is the same thing O_o) sounds as:

"Who finds a friend, finds a treasure."

"Under the rainbow" there's the treasure for them, Teito and Hakuren are the treasure of the other one, so isn't this title perfect for them?