Trust me, I tried so hard to get rid of that square. It's located in the layout file.
I tried:
Resize it to zero. Didn't work.
Move it to off of the screen. Didn't work too.
Replace it with the pattern that you use in the background (in you example) and sort of work, but the generated square is a bit blurry compared to the background, so that didn't work.
That square has an image format that has not transparency, so I wasn't able to make it transparent. Another think that didn't work.
Another alternative would be to modify the code.bin and remove that image rendering. I decompilled the code.bin but I wasn't able to understand a thing
(maybe someone can help us on this?)
So what I can do for now is to replace that square with a black square. And let the user to make a frame but that frame does not have to be filled in all the screen. The frame should be in this way:
Again, this is the best I can do for now with my knowledge