From the menu bar click on Format and
choose Background.
Click on the down arrow and select
a color that is available or click on More Colors or Fill Effects.
This is the window for More Colors. You
may choose a color that is available or click on the Custom tab and
choose a color from that window.
This is the window you will see
if you choose Fill Effects. You may select a gradient (with up to
two different colors), a texture, a pattern, or use a picture from
a file.