The reason what you’re trying doesn’t work the way you want it to, is because not(choice_nightmode) essentially means “anything/everything except nightmode”, which the sepia and white backgrounds both fall under.
You’d have to know the “name” of the other two backgrounds to go the route you’ve tried. I’m not sure if either have names, but I’ve never checked.
I have tried every method mentioned here but my images always show up on the wrong background.
I have switched the name of the images in the program many times to see whether I am writing the program wrong, but it seems to show up of the same colour as the background every single time. No matter what I do!
Can anyone guide me, if its not too much to ask?