The cluster legend allows you to quickly determine which classes in the view belong to which clusters in the system by changing the colors to match those of cluster assigned ones. Pressing the legend button will display a list of all the clusters in the system for which at least one class is visible in the view. Next to each cluster name is a color, and pressing the top right color square will automatically set a unique color for each cluster and change the classes belonging to that cluster to match. Pressing again the legend button will hide it from view. The image below shows the legend in use and the classes colored.
Tip: Use the cluster legend also to quickly see sub-cluster organization within your overall cluster design.