Some plot types have additional color handling to facilitate easier handling and differentiation between data sets.
Pie plots support the concept of color-themes. A color theme is simple a set of colors used for consecutive slices within the Pie. How to specify color-themes is further discussed in Section 16.1.9.
Matrix (Only available in the Pro-version) and contour plots also
                                have the concept of color maps. This is a range of colors used to
                                indicate the data in the plot. Examples of color maps can be found
                                in Section 22.8. (Color maps are defined
                                and implemented in
                                "jpgraph_colormap.inc.php").