Cannot set color for vignette 3D effect

I add a vignette 3d effect to sceneEnvironment. 

When I change the color of the effect in Properties, and run the app I get an error:

Invalid property assignment: 3D vector expected

In the QML code I can see that the vignetteColor property has been added but it has no value:

Vignette {
    id: vignette
    vignetteColor: ""
}