code: public <T,E extends TypedEdge<T>> void write(
                          Multigraph<T,E> g, File f, Map<T,Color> edgeColors) 
                          throws IOException {
          write(g, f, edgeColors, true, null, false);
      }
docs: Writes the provided multigraph to the specified {@code gexf} file, using
  {@code edgeColors} as a guide for how to display parallel edges of
  different types.
  
  @param f the file where the {@code gexf} graph will be written.  Any
  existing file contents will be overwritten
  @param edgeColor a mapping from an edge type to a color.  Types that do
  not have colors will be randomly assigned one and the {@code
  edgeColors} map will be updated appropriately.