Change color button background

GoJS
#1

i’m little new with go js and i don’t understand how, is its possible, i can change a color button background or just the shape inside it,

my proble is assing to a node the color shape but i don’t understand how

my button (inside a node)

            $("Button",{click: changeColor},
              $(go.Shape,
                { fill:  'red', stroke: null, desiredSize: new go.Size(20, 20) },
                new go.Binding("fill", "color").makeTwoWay()
              )

this is my function

function changeColor(button) {
  var node = button.part.adornedPart;

  var shape = node.findObject("SHAPE");

  node.diagram.startTransaction("Change color");

  shape.fill = button.shape.fill; //<- doesnt work 

  node.diagram.commitTransaction("Change color");
};
#2

Call Model.setDataProperty. There are lots of examples throughout the documentation and the samples.
http://gojs.net/latest/intro/dataBinding.html#ChangingDataValues