A color scheme 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 schemes 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 schemes. Simply choose the ribbon command Design | group Scheme | Color scheme 
, select a suitable color scheme and apply it. Two examples of color schemes are illustrated in the following screen images.
A presentation with a green color scheme
The same presentation after applying a different color scheme
For more information on color schemes, see Changing slide color scheme and background.