How to Apply Themes to Your PowerPoint 2013 Masters
You can use the Edit Theme group in the Slide Master tab on the Ribbon in PowerPoint 2013 to change the theme applied to a Slide Master. Note: All the layouts that belong to a given Master use the same theme. So, it doesn’t matter whether the Slide Master itself or one of its layouts is selected when you change the theme; either way, the entire Slide Master is changed.
To change the theme for a Slide Master, follow these steps:
Choose View→Presentation Views→Slide Master or Shift+click the Normal View button at the bottom right of the PowerPoint window to summon the Slide Master.
Use the Themes drop-down list on the Slide Master tab to select the theme you want to apply to the Slide Master.
(Optional) Use the Colors, Fonts, and Effects controls to modify the color scheme, fonts, and effects used for the theme.
Treat yourself to a bag of Cheetos if it works the first time. If it doesn’t work, have a bag of Cheetos anyway. Then rub all that orange gunk that sticks to your fingers on the computer screen. That will apply the Cheetos Orange color scheme to your Slide Master — at least temporarily.
If you want to adjust the slide background, use the Background Styles control.