"Rainbow" is a piano ballad in the key of E-flat major with a slow tempo of approximately 64 beats per minute.

[2] The song was penned by Musgraves with Shane McAnally and Natalie Hemby six years prior to its release as the closing track on Golden Hour.

[5] For the performance, Musgraves donned a simple white gown and was accompanied by a pianist playing a rainbow piano behind her.

[8] In it, various characters are shown in different rooms of a dimly lit house, including "a single mother taking care of her child, a man facing his alcohol abuse, a young person wrestling with gender identity, and a teenager caught in the middle of a family crisis.

"[8] Scenes of Musgraves performing the song either accompanying the others or alone are mixed in throughout the video and near the end she is seen sitting on the floor of a room surrounded by lush greenery and flowers as a rainbow appears overhead.