Various schools of thought JB. A backscene is not actually meant to draw the eye - as its name implies, it’s only there to set the scene, so is not meant to be too detailed, otherwise you look at it before the model! As Phil says above, a suggestion of sky might even be enough. What you are actually trying to do is make the brain ignore the surroundings of the layout - ie the room, walls etc, and focus on the model. Barry Norman has a simple technique in his book involving graduated bands of blues greens and browns which worked for me….