Oh, strange. Are you using the gameboy or gameboy color rom? And which version?
That was the gbc rom, I tried the gb rom just now and with that the screen is entirely black, although the music and sound effects still play. I just downloaded them a couple days ago so they should be the current version.
Doing some more attempts at playing it and it gets wierder - most of the time sprites are black when still and yellow when moving, but occasionally on moving to a new floor, they will be dark grey when still instead, so at least I can see them. And dying and starting a new run tends to scramble all the colors of the sprites, background, and menus up as well! This flashcart does not seem to like this game.
Yeah, that sounds really weird! I know that it worked on real hardware at some point, since it was tested for the competition. But it's possible that I broke something since then. I also realized that the itch.io version was out-of-date and has a couple of bugs that have been fixed, so I've updated to v1.0.9. Maybe that will work better?
Thanks for letting me know either way!