To add some extra visual interest to your document, add a background color using the Page Color button. You can also add a picture as a background watermark.
Change the background color
Click Design > Page Color.
Pick the color you want under Theme Colors or Standard Colors.
If you don't see the color you want, click More Colors, and then pick the color you want using any of the options in the Colors box.
To add a gradient, texture, pattern, or picture, click Fill Effects, and then click the Gradient, Texture, Pattern, or Picture tabs to select the options you want.
Patterns and textures are repeated (or “tiled”) to fill the entire page. If you save your document as a Web page, the textures are saved as JPEG files, and the patterns and gradients are saved as PNG files.
Remove the background color
To remove the page color, click Design > Page Color >No Color.