Background graphics tend to be the largest 2D graphics in any app. They can take up a lot of room and make an app overloaded. On my most recent project I tried to create graphics that could be changed and modified in many different ways with very few graphics to create a variety of backgrounds.
For these backgrounds I created a painted texture that can be layered over a single color to create a painterly, watercolor look. I then created tileable patterns to layer on top to add even more variety.