rlist-color pairs
            if isinstance(mark_groups, dict):
                # Dictionary mapping vertex indices or tuples of vertex
                # indices to colors
                group_iter = iter(mark_groups.items())
            elif isinstance(mark_groups, (VertexClustering, VertexCover)):
                # Vertex clustering
                group_iter = ((group, color) for color, group in enumerate(mark_groups))
            elif hasattr(mark_groups, &#34;__iter__&#34;):
                # Lists, t