By 1999, “All That Glitters,” film in which Mariah had the lead role, was in the pre-production stage. Part of the agreement was that Mariah would also be in charge of the soundtrack. The songs were to be inspired by the movie. The movie takes place in the 1980s and, therefore, the sound would also incorporate elements that were popular during this decade. Carey had already started working on the soundtrack when she was told the production was stopped. Carey, disappointed and in the middle of the recording process of the new album, decided to use the songs she had for a brand-new studio album. For the first time, Mariah traveled to the island of Capri, Italy to work on her music. She claimed Capri allows her to disconnect herself from the outside world and focus on her music.

“Heartbreaker,” the lead single, would easily fit this new project. Rainbow turned out to be an album heavily oriented toward urban sounds. Carey enlisted a big number of collaborators. Guest artists included Jay-Z in “Heartbreaker,” Da Prat and Missy Elliot in “Heartbreaker (Remix),” Snoop Dogg in “Crybaby,” Mystical and Master P in “Did I Do That?” and Usher in “How Much.” The album also consisted of a duet with Joe and a special appearance by boy-band 98 degrees, “Thank God I Found You.” Inviting other artists to collaborate with her was something that, according to Carey herself, she was not allowed in her previous albums.

In Rainbow, Mariah Carey found an opportunity to release many of the feelings that overwhelmed her since her divorce. Mariah had in fact achieved creative freedom which she was eager to showcase in the new album. Lyrically, Rainbow was one of her most personal albums. “Thank God I Found You” became her own personal way to express her happiness and satisfaction in terms of relationships. “Petals” alludes to the dysfunctional situation she undergoes along with her family. “Can’t Take That Away (Mariah’s Theme)” makes reference to the harsh situation with Sony Music Executives. The latter was originally written after the Columbine incident where several students were shot in a New York City high school.

As in almost every studio album of hers, Mariah included a cover of an an old song. This time, she remakes Phil Collin’s “Against All Odds (Take a Look at me now).” Urban jams are an important element in Rainbow. With the recruitment of urban stars and producers it was obvious that Carey would not be returning to the mainstream pop that characterized her in the beginning of her career. There was an obvious evolution that started with 1995’s Daydream and became more evident with 1997’s Butterfly. Now, Mariah took her music to a whole different level, which allowed her to differentiate herself from other female pop acts.

The heartbreaking ballads were essential. Mariah initially considered Walter Afanasieff to help her create the ballads. Afanasieff, who became an extremely requested producer largely because of his work with Mariah, was unable to work with Mariah. Speculation started that the real reason Afanasieff was not working on Mariah’s album was due to Tommy Mottola’s attempt to boycott Mariah’s career. Creative differences between Carey and Afanasieff seemed to be the main reason for the end of the professional relationship. Now that Walter Afanasieff was, for the very first time, not part of a Mariah Carey album, it was time to enlist other producers. David Foster, a top producer who had many hits to his name, was eager to collaborate with Carey. With Foster, Mariah shaped “After Tonight,” a song that combined the nostalgic sound of an acoustic guitar with Carey’s airy voice to express feelings of desolation when somebody loved is about to leave.

It was not Foster but legendary producers Jimmy Jam and Terry Lewis who replaced Walter Afanasieff. Both producers were more R&B oriented that their predecessor, which fit Carey’s new musical path. When discussing her work with Jam and Lewis during an interview for Launch Magazine, Mariah took the opportunity to take a shot at Walter, “I think Jimmy and Terry have added a different direction musically. I told them how great it was to be able to sit there (in the studio) and not have to say: No, not so schmaltzy.” With this album, Mariah felt confident making decisions and taking her music toward the musical direction she had visualized.

The album’s vibe is joyful, often changing the mood after a melancholic ballad. Mariah has often stated that she named the album Rainbow for two reasons, one being her message of hope for the new millennium and the other being the representation of the different musical genres that shaped this album. In the booklet, Mariah said that “this album chronicles my emotional rollercoaster 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 critics were mainly positive for Carey’s Rainbow. Rolling Stone called the album “a sterling chronicle of accessible hip-hop.” Other sources praised Carey’s ability to successfully blend R&B and Hip Hop. At this point, pop acts were mimicking Mariah’s trend in terms of music. “Thank God I Found You” was nominated for the 2001 Grammy Award for Best Pop Collaboration with Vocals but, after the Daydream Grammy debacle, she refused to attend the ceremony.

Commercially, Rainbow was another solid album, debuting at number two on the U.S. Billboard 200 Albums chart with 323,000 copies sold, the highest first-week sales of her career at that time. Despite strong sales the following weeks, the album could not enter the top position because of Faith Hill’s album Breathe. Rainbow managed to stay in the top twenty for ten weeks and on the chart for thirty-five weeks, re-entering the chart one time. Rainbow’s sales peaked at 369,000 copies in its eight week. Rainbow was been certified three times platinum by the Recording Industry Association of America. In America, these numbers resulted low compared to Carey’s previous albums, and many started arguing that the sales of her albums were steadily going down. However, the records that Mariah broke with Rainbow overshadowed these assumptions.

When “Heartbreaker” topped the U.S. charts, Mariah achieved her fourteenth #1 single, record that she broke again when Rainbow’s second single, “Thank God I Found You,” topped the Billboard Hot 100 chart for a week. “Heartbreaker” also allowed Mariah to break a record set by the legendary Beatles, accumulating a career total of sixty weeks at #1. In 2000, Mariah re-released Rainbow in Europe now including a new version of “Against All Odds” with Irish boy-band Westlife, her second #1 hit in the U.K. Internationally, the sales of Rainbow were equally impressive to those from the United States, reaching the top 5 in most markets, hitting the #1 spot in France and on the United World Chart. Worldwide, Rainbow has sold approximately twelve million copies.

Mariah seemed optimistic with Rainbow and the success of the project, but her issues with Sony Music had become intolerable. Rainbow became Mariah's last album with Sony Music; several issues emerged, including the label's attempt to cancel further singles from the album despite the first two single's success. Carey could release two more singles in the United States, “Crybaby” and “Can’t Take That Away (Mariah’s Theme).” The latter was also alluded to her struggles with Sony Music executives, more specifically with Tommy Mottola.