I left the box in its original white colour but made the inside look like a Photoshop transparent layer:
With a few prints on top it really does resemble Photoshop quite well:
There are many different images you can create after:
I am really happy with the results. And I enjoyed every moment of this project creative process. Screen print was a new thing for me and I am so exited to have this skill now. Of course, there is so much more to learn, but I believe I wont abandon the screen print and only improve in the future.