PowerPoint uses professionally designed color schemes.  To change the template for color or black and white overheads, from the Format menu, choose Slide Design.  From the Slide Design pane, choose slide Color Scheme.  Select a light background color scheme for either color or black and white and click OK.

To change the colors in the color scheme, click Edit Color Scheme at the bottom of the Slide Design window.  Make changes in the Edit Color Scheme window and click Apply.