Do not set a full-screen, solid background color this way
- Switch to the slide master view (or, if you wish to change only one slide, the slide view).
- Turn on the Drawing toolbar.
- Insert objects.
- Select the objects.
- Choose Draw → Order ? Send to Back so that the objects are behind the text placeholders.
You should then configure the background color scheme color to be a color that reflects an "average" of your background. For example, if you are using a photo that has a lot of dark green, set the background color scheme color to a dark green.