Kacey Musgraves, left, and Willie Nelson perform "The Rainbow Connection" at the 53rd annual CMA Awards at Bridgestone Arena, Wednesday, Nov. 13, 2019, in Nashville, Tenn. (AP Photo/Mark J. Terrill)
"Rainbow Connection" was written by Paul Williams and Kenneth Ascher for the 1979 film The Muppet Movie. The song, originally performed by Kermit the Frog (voiced by Jim Henson), has been covered multiple times throughout the years. Nelson recorded the song for his 2001 album Rainbow Connection.
Nelson and Musgraves previously collaborated on the duet "Are You Sure?," which was featured on Musgraves' sophomore album Pageant Material and "A Willie Nice Christmas" from Musgraves' holiday album A Very Kacey Christmas.
Musgraves won Female Vocalist of the Year at this year's CMA Awards. She was nominated alongside Kelsea Ballerini, Miranda Lambert, Maren Morris and Carrie Underwood. She also earned a Song of the Year nomination for "Rainbow," along with co-writers Natalie Hemby and Shane McAnally.