code: protected boolean visitMe(VertexType vertex) {
          return (getColor(vertex) == WHITE) && (vertexChooser == null || vertexChooser.isChosen(vertex));
      }
docs: Predicate to determine which vertices should be visited as the search
  progresses. Takes both vertex color and the vertex chooser (if any) into
  account.
  
  @param vertex
  the vertex to possibly be visited
  @return true if the vertex should be visited, false if not