code: public N getPartitionSuperNode(N node) {
      checkNotNull(colorToNodeMap, "No coloring founded. color() should be called first.");
      Color color = graph.getNode(node).getAnnotation();
      N headNode = colorToNodeMap[color.value];
      if (headNode == null) {
        colorToNodeMap[color.value] = node;
        return node;
      } else {
        return headNode;
      }
    }
docs: Using the coloring as partitions, finds the node that represents that
  partition as the super node. The first to retrieve its partition will
  become the super node.