You can also adjust the slide background in the Master view.
From Slide Master view, select the slide master or one of the layouts.
Right-click the slide and select Format Background.
Edit the background.
The options that appear in the Format Background pane will vary depending on which theme you are using. You will frequently see Fill, Hide background graphics, Color, Transparency, Line, and Insert Picture.
Click the Close button in the Format Background pane.