Whited out the backgrounds. Enjoy!
Ha. Same problem, but now they have white backgrounds. I suppose it's an alpha thing.
Something to note: Running VGA tiles with no scaler causes those pngs to also have a black background, but the EGA tiles are consistently fine.
Anyway, see what you can do with GIMP.
Test it out with a single up ladder first, run the snapshot, cheat mode F3 to destard and light a torch.
An issue i have with all ladder tiles (even the sacred c64 version) is that they don't respect the perspective illustrated in the orientation of the dungeon walls.