To understand how themes are used, it is easiest to look at the sample code. For example, the Aqua Theme can be applied using the following.
1 2 3 4  | $theme_class = new AquaTheme(); $graph->SetTheme($theme_class);  | 
In line 1, an instance of AquaTheme class is created, and the graph theme is changed by passing the instance to SetTheme(). To use 'GreenTheme' instead of 'AquaTheme', use the following.
1  | $theme_class = new GreenTheme; | 
All theme classes inherit the abstract 'Theme' class.