A color theme is a predefined set of matching colors for different parts of your slides, such as background, title, text and lines, hyperlinks or fill areas.
These color themes enable you to quickly and easily change all colors of a presentation without having to do so individually for each element of the presentation.
Each slide design already includes several predefined color themes. Simply choose the ribbon command Design | group Theme | Color theme 
, select a suitable color theme and apply it. The following screenshots show two examples of color themes.
A presentation with a green color theme
The same presentation after applying a different color theme
For more information on color themes, see Changing slide color theme and background.