I spent most of last night tweaking the graphics.
For starters, I've jigged about the whole Background tileset.
If you've bothered to poke around inside the old game, you'll have noticed that bg.png contains a great big pile of unused "Inside a Wall" stuff. It was originally going to serve a purpose, and fill out the black, but eventually I decided that having plain black nothingness would be good enough, and the black stayed as black.
So, they're now removed from the tile...