We would like to render a Graphviz node as a color key to types. Maybe use html label? edotor 
digraph { Graphviz [shape=plain label=<<table border="0"> <tr><td bgcolor="white">Page Colors</td></tr> <tr><td bgcolor="bisque">Prompt</td></tr> <tr><td bgcolor="lightblue">Page</td></tr> </table>>] node [style=filled fillcolor=lightblue] draw [fillcolor=bisque] walk -> map -> draw -> walk }
Darn. This html label renders as promised in edotor but not in our own Graphviz plugin above.
Graphviz [shape=plain label=<<table border="0"> <tr><td bgcolor="white">Page Colors</td></tr> <tr><td bgcolor="bisque">Prompt</td></tr> <tr><td bgcolor="lightblue">Page</td></tr> </table>>]