The phrase "to paint the background" means to provide context or background information about a situation or story. It is like setting the stage for the main events or information. Full definition
For 1998 graphics they are awesome, nice hand painted backgrounds and spectacular 2D animations, but unfortunately it is 2009, and the retro vibe just feels off for spending the dough. (snackbar-games.com)
In her artworks, she pulled figures from movie posters, magazines, and advertisements, and set them against boldly colored painted backgrounds. (garthgreenan.com)