Change a window’s background color in Preview on Mac
Preview shows a gray background behind PDFs and images. In a PDF or image, you see the background if you expand the window larger than the size of the document; in an image, you can also see the background through any transparent sections. You can change the background color.
Go to the Preview app
on your Mac.Choose Preview > Settings, then click General.
Click the “Window background” color well, then choose a color.