Prism Island

Prism Island is the main setting of the game Paper Mario: Color Splash. The island is first found drained of half its colors. Mario, Princess Peach and Toad came here to solve a mystery about a colorless Toad, after noticing that the stamp on him is the same on the Prism Island map in the Mario Bros.' House.

On the island is a Bowser Tape, implying that Bowser is responsible for the colors now gone. This was later confirmed on the September 13 episode of Nintendo Life, with it also revealing that Bowser had been covered by black paint and intended to share the dark gift of it (although Princess Peach in her message to Mario upon being kidnapped implied that Bowser was not himself).

Prism Island is shaped like a giant paint brush, and the color arrangement is arranged in a palette formation. Similarly to how the areas of the Beanbean Kingdom are named after onomatopoeias for laughter and the areas of Pi'illo Island are portmanteaus of items associated with sleep, many areas of Prism Island are named after various colors.

Entertainment
Toads celebrate a day called "Oceanfest", where they participate at multiple games to win a key as the first prize, allowing the winner to enjoy the beach.

Trivia

 * With each Big Paint Star recovered, the map's theme adds more instruments as well as going up a half step in pitch.