I’m still looking for a way to change the background color of the Windows 10 Photos APP, but this did work for the standard Windows Photo Viewer that came with Windows 7 and up…

When you open a picture file in Windows Photo Viewer the default background color is [off]-white. This is just fine in most use cases. But you might find yourself in a situation where your picture is very

Source: How to change the background color in Windows Photo Viewer – Super User