Sia wrote and recorded this uplifting tune for the My Little Pony: The Movie soundtrack. The song, sung by her Pegasus pony character Songbird Serenade in the film, is about comforting someone through their pain. The hopeful lyrics talk about how despite all the hardships the ponies have suffered, if they persevere until the end the sun will come out again.

The video, directed by Daniel Askill, features Sia's favorite muse, young dancer Maggie Ziegler. Sia and Maddie first collaborated on the clip for "Chandelier," and since then she's starred in the clips for "Elastic Heart," "Big Girls Cry." "Cheap Thrills" and "The Greatest." We also get to see Sia's Songbird Serenade character belting out the song for her pony friends.

Asked by Billboard about the meaning behind her dance in the video, Ziegler replied:

"The story that I was telling in 'Rainbow' was that in the beginning I was discouraged, because there was no rainbow, and I lost all of my magic, and I just kind of felt defeated. And then I finally see a spark, start to believe in myself, and I finally realize that everything is okay -- and if I keep believing in myself, then everything will work out perfect. 'Cause that's when the rainbow comes out, and I was super happy because I feel like all of my magic has come back. Basically, this is all about making your dreams come true, and having that passion and believing in yourself."