For a better understanding of Gephi for visualizing graphs I used a dataset freely provided by Rebrickable. Combining the color information and themes from the Lego© sets in that database Gephi can be used to visualize which colors are used in which themes and vice versa.
Here is the result Lego© Colors and Themes.

Click the image for an interactive version. Thanks to Rebrickable for the dataset, Gephi for the awesome graph software, sigmajs for the Javascript library dedicated to graph drawing and the Oxford Internet Institute for the Gephi Export plugin.