I would have liked to do that, but unfortunately it’s not possible. The black screen is actually when the maze is being drawn, then the colour is changed to reveal the new room.
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Great game! About the rewriting of the screen we use for instance for some games a memory buffer so we draw the screen first in that buffer and then move it to the screen. It implies having enough free memory for that purpose and of course that is difficult if the game requires the whole available space. Another option would be an attribute fadeout + fadein so the cut to black is progressive. We use that effect on our Area 51: Roswell Incident game, it could be a nice option and the size in bytes of the fadeout asm is very small. Cheers! :)