Before you can begin painting the background, you should draw the illustration first. This will ensure you stay on track with your intended idea as you paint. Mark the outlines of the shapes you wish to draw. For instance, if you are drawing a forest, use cylinders for the trunks of trees. Create shrubs with a curved semicircle shape. Add the texture of the shrub by making the curved line dip in and out. Draw pockets of grass with small curved triangular shapes.
Paint the midtones for your background. Midtones are the mid range colors that are neither overly bright nor especially dark. For tree trunks, you should use a medium brown. Use green for the grass and a deep forest green for the shrubbery. Paint dark brown for the background to give the forest the illusion of depth.
Highlights and shadows will give your anime background extra detail. This will also set the cell animation apart from the background. This is because the cell animation uses simple highlights and shadows, while the background can use complex blending and shading. Select a color that is a few shades lighter than the midtone to add highlights. If you are using watercolor, you will need to use colored pencils to create highlights. Consider your light source before adding highlights. Your light source is the direction that the light is coming from. For example, if the sunlight is coming from the upper left-hand corner, you will need to add highlights to the tops of objects as well as a thin line of highlights along the left side. Add shadows with darker versions of your midtones. Place these where the light source would have trouble reaching. Blend the highlights into the midtones by wetting your brush and slowly pulling a small amount of highlight paint into the midtone area. Do the same for the shadows.