Changing the background color of slice views

I am not being able to change de slice views background colors. I am doing this:

viewNode = slicer.app.layoutManager().sliceWidget('Red').mrmlSliceNode()
viewNode.SetBackgroundColor(1,1,1)
viewNode.SetBackgroundColor2(1,1,1)

But it has no effect. What should I do? I want to change to white. Thank you!