How to change the colour behind the image in Lightroom

Is there any way to change the colour behind the image in Lightroom?

I don't mean the "background" border area around the image, which I know I can change in the "background" panel of the "Interface" tab under Preferences.

I mean after I've applied "Transform" settings to correct perspective distortion, the edges of the image are not straight or level, and I get slithers of white in the corners.  If the sky in the photo is white, it can be hard to see where the image ends and the empty gap starts.  Is there some way to change the colour of these areas to a different colour than white, or to the checker board pattern often used to represent a transparent area?