Baz,
I asked the Mrs to do a number of background paintings. I measured out the dimensions on a large sheet of art paper and drew a light horizon line on each panel.
Since it is a matter of removing seven screws to gain access to the background I didn't remove the one that is in at the moment. I would describe it as having a brighter sky with more yellow and gold , suggesting a sunset.
Here are the others. The tops were left blank as they curve into the top to reflect light.
Best
Les