Changing Color Schemes
Click Format | Slide Color Scheme in PowerPoint 2000 or in PowerPoint XP, click Format | Slide Design and select Color Schemes from the design view on the right.
Click first color scheme in the second row.
Click Apply to All.
Note: Use a background color that matches the lighting in the room where you plan to present, i.e., dark blue for a darkened room and a lighter for a lighted room.