How can I set the linkingTool's Temporarylink Arrowhead color?

myDiagram.toolManager.linkingTool.temporaryLink.path.stroke = ‘white’; works nicely to set the link color, but the arrowhead is still blue. How can I change the color of the arrowhead as well?

myDiagram.toolManager.linkingTool.temporaryLink.elt(1) would get you a refernce to it.

But perhaps you should just create a new temporaryLink that you find agreeable:

myDiagram.toolManager.linkingTool.temporaryLink =
    { layerName: 'Tool' },
    $(go.Shape, { stroke: 'blue' }),
    $(go.Shape, {
        toArrow: 'Standard',
        fill: 'blue',
        stroke: 'blue'

That’s the default definition, if you want to customize it from there.