Question: Kesha's fourth headlining concert tour supported what studio album of hers?
Context: The Rainbow Tour 2017 is the fourth headlining concert tour by American recording artist Kesha.  The tour is in support of her fourth studio album, "Rainbow", and is her first solo tour since the Warrior Tour in 2013.  The tour started in Birmingham on September 26, 2017, and concludes in Oslo on December 16, 2017.  Tickets for this tour range from $42 to $2,484 on the secondary ticket market. The Summer Break Tour was a headlining concert tour by American pop boy band, Big Time Rush that featured American pop artist, Victoria Justice.  This was Big Time Rush's third consecutive headlining tour, and Justice's second overall tour.  The tour supported Big Time Rush's third studio album "24/Seven" and Justice's music from the television show "Victorious".  The tour played 40 shows in North America. The Addicted Tour was the fourth headlining concert tour by American pop-rock recording artist Kelly Clarkson.  It was a United States tour beginning on June 30, 2006, in West Palm Beach, Florida and ended on August 6, in Auburn, Washington.  The tour was in support of her sophomore studio album, "Breakaway" (2004), following the Hazel Eyes Tour (2005) and Breakaway World Tour (2005–06). Rainbow is the third studio album by American singer Kesha.  It was released on August 11, 2017, by Kemosabe and RCA Records.  On July 5, 2017, Kesha announced via her Instagram account that she was releasing a single, titled "Praying".  The song was released alongside its accompanying music video and the album's pre-order. The 8123 Tour is the fourth headlining concert tour by the American rock band The Maine, in support of their fourth studio album "Forever Halloween" (2013).  The tour currently consists of 37 shows in North America.  The tour kicked off at a free hometown show at Tempe Marketplace in Tempe, Arizona. The On the Road Again Tour was the fourth headlining concert tour by English-Irish boy band One Direction.  It promoted the band's fourth studio album, "Four".  The tour began on 7 February 2015 in Sydney, Australia and ended on 31 October 2015 in Sheffield, England.  The majority of the tour venues were sold out, bringing in revenue of $208 million from 80 shows total. The Kill the Lights Tour was the fourth headlining concert tour by American country music artist Luke Bryan.  The tour is in support of his fifth studio album "Kill the Lights" (2015) and began on February 11, 2016, in Evansville, Indiana.  The tour played before 1.6 million fans in 2016.  The tour's second leg began on February 16, 2017, in Huntington, West Virginia and ended on March 18, 2017, in Orange Beach, Alabama. ArtRave: The Artpop Ball (stylized as artRAVE: the ARTPOP ball) was the fourth headlining concert tour by American singer Lady Gaga.  Supporting her third studio album "Artpop" (2013), the tour ran from May 4, 2014 to November 24, 2014.  The tour dates included cities where Gaga had canceled shows of her previous Born This Way Ball tour after suffering a hip injury.  The ArtRave tour was preceded by a performance at the South by Southwest music festival, which drew controversy due to a segment where an artist vomited on Gaga, and a seven-day residency at the Roseland Ballroom in Manhattan, New York. The Demi World Tour was the fourth headlining concert tour by American singer Demi Lovato.  It was Lovato's second tour in support of her fourth studio album "Demi" (2013), following The Neon Lights Tour.  During most of the European tour dates in 2014 (except for Istanbul), Lovato was the opening act for Enrique Iglesias' Sex and Love Tour.  The tour was produced and promoted by Live Nation, and sponsored by the Tampax and Always Radiant Collection.  The first leg of the tour took place in the United States and Canada from September 6, 2014 to October 27, 2014, where Christina Perri and MKTO served as opening acts.  Lovato toured Oceania and Asia in early 2015. The Warrior Tour was the second headlining concert tour by American recording artist Kesha, in support of her sophomore studio album, "Warrior".  The tour started in Boston on May 23, 2013 at the Comcast Center.  After the first North American leg, the tour went to Europe in July 2013, and then came back to North America for another leg in August and September 2013.  The tour then played various shows in Asia and North America in the Fall of 2013.  The first North American leg, with the exception of June 8, 2013 and June 29, 2013, was co-headlined with Pitbull and referred to as the 2013 North American Tour.  A planned Australian leg was also going to be co-headlined with Pitbull, but was cancelled by the promoter two weeks before the leg started.  Many shows of the tour are a part of festivals including Live at the Marquee in Cork, Ireland, the Wireless Festival in London, England, and the Illinois State Fair in Springfield, Illinois.  In October 2014, Kesha brought back the Warrior Tour setlist and costumes to perform for a music festival in Shanghai, China.  After that, the tour was revisited and traveled throughout South and North America with new songs, visuals, and costumes added to the tour through January to September 2015.
Answer: Rainbow