If you want to apply the change to selected slides only, select the slides in normal view. Otherwise, the change applies to all slides that follow the design template of the currently selected slide.
On the Format menu, click Background.
Select a color from the color scheme
Select a color outside the color scheme
Select a fill effect or picture
Use the background fill
from the slide master
Tip
If you want to hide the background graphics that are on the slide master, click the Omit background graphics from master check box.