How to change the pink selection box?

How do I change the color of the pink box and blue arrow here?

I have tried this code: =
    $make(go.Part, { layerName: 'Tool', selectable: false },
        $make(go.Shape, { name: 'SHAPE', fill: null, stroke: 'red', strokeWidth: 2 })

But it has not worked. Thanks for any help you can provide!

This is covered by the Introduction page about Tools: GoJS Tools -- Northwoods Software.

In particular, look at: GoJS Tools -- Northwoods Software

Perfect thank you!