define your model like this:
DiGraph [
node "a" [ Shape Diamond, Style Filled, FillColor red ],
node "b" [],
"a" ==> "b",
"a" ==> "d",
Subgraph [
node "d" []
]
]can be rendered using toText to:
digraph {
a [shape=diamond ,style=filled ,fillcolor=\"#f44336\"];
b [];
a -> b;
a -> d;
subgraph {
d [];
}
}