The plan was for every single background of the film to be completed in a very painterly style, with thick, visible brushstrokes and bright colours.
Part 1: Skyspheres
Part 2: Grass and trees
As you can see, like the skyspheres, the ground, grass and bark textures are all incredibly painterly with large, distinctive brushstrokes.
As we can see in these render tests, the 2-Dimensional painted background almost make the setting look like a stage for the action to take place on.
As we can see in this render test, the characters and the background appear to belong in the same art style, but the rabbits stand out from the rest of the assets with painted features because their textures are a lot smoother.