Here is my visitor after making the suggested changes. I am not sure this does the job because I don't understand the following: 1) How is a custom visitor used as a replacement to depth_first_search? The code for how to handle the coloring of the vertex nodes seems to be handled by the depth_first_search algorithm and not the associated visitor. 2) When is the operator() called? Stephen -------- CODE -------- template <class VertexType, class Graph> class filter_visitor : public boost::base_visitor< filter_visitor<Visitor> > { private: typedef on_discover_vertex event_filter; public: filter_visitor (Graph const& g) : m_color (internal_map (num_vertices(g))) {} template <class Vertex, class Graph> void operator() (Vertex child_node, Graph& g) { Vertex parent_node = g[child_node].get_parent_node(); typename graph_traits<Graph>::edge_descriptor e = edge(child_node, parent_node, g).first; g[child_node].send_message (g[parent_node].get_object(), g[e]); } private: ColorMap m_color; };