Rainbow is a collaboration-heavy album on which Carey worked with a wide range of producers and artists that dominated the music scene of the late 1990s; Rolling Stone called the album "a sterling chronicle of accessible hip-hop balladeering at the close of 1999." Guest artists included rappers Jay-Z, Da Brat, Missy Elliott, Snoop Dogg, Mystikal and Master P, singers Usher and Joe, and boy band 98 Degrees. The album was the first since Carey's debut to not be co-produced heavily by Walter Afanasieff, her long-time collaborator who co-produced most of her signature ballads. In his place, Jimmy Jam and Terry Lewis were enlisted. Many felt the album was a natural continuation of the R&B and hip hop sounds Carey had explored on the album Butterfly (1997).
Rainbow is often considered one of Carey's more personal albums alongside Butterfly and Charmbracelet. The message from Carey in the insert reads,
"This album chronicles my emotional roller coaster ride of the past year. If you listen closely, there's a story here with a very happy ending. After every storm — if you look hard enough — a rainbow appears."
The review of the album by Entertainment Weekly asserts that "Against All Odds (Take a Look at me Now)" refers to her relationship with Derek Jeter. "Petals" makes several obscure references to a "dandelion", siblings, and a "Valentine". Many conjecture that "Valentine" refers to Carey's ex-husband, Tommy Mottola, who at one time had the stage name of "T.D. Valentine". Some speculate that the "siblings" refer to Mottola's children and the "dandelion" refers to Carey's sister Allison, a prostitute.