Change the slide background
1) Select the 'Format' menu and select 'Custom Background...'. (The Custom Background dialog box appears.)
2) Select the desired color and style from the drop-down list box in the 'Background Fill' group.
3) (Optional) Check the 'Omit Background Graphics from Master' check box.
4) (Optional) Choose the 'Preview' button, to view the changes without accepting them yet.
5) Do one of the following:
a) Choose the 'Apply to All' button, to apply the changes to all the slides in the presentation.
b) Choose the 'Apply' button, to apply the changes to the current slide only.
c) Choose the 'Cancel' button, to cancel the changes.