Possibility to colour levels?
Add some variety into the game
I love how the tower, and the underwater cave, really look different from the rest of the game. I was wondering whether it might be worth colouring all levels to some extent or another? Just a pallete swap would be great, I think. Bit of a green shade here, bit of red there. Saving the purple for deeper levels where corruption is stronger, etc.
In the old 8-bit era of games, a bit of colour variation really brought recognition to levels that would otherwise have looked and felt exactly the same, and I can't help but feel a bit of the same would help brighten ADOM. I'm not trying to suggest anything as extreme as the tower or the water temple, just an option of slightly varying the palette based on dungeon level to mix things up a little, and bring a little recognition to those same old levels. For example, recognising that unusually dirty D:5, or the weird, pinky colouration of the brick on D:13, where higher metal items start becoming common...
Further suggestion / fleshing out based on ideas and comments: I agree with tkoyah, that it would be nicer if each dungeon had a slightly different tint - Assassin's guild, dwarvern graveyard, high kings, Uninteresting dungeon, rift dungeon, darkforge etc, but were uniform in colour across the dungeon in question.
Special case perhaps being made for CoC, which could get darker and more purple the deeper the player ventured down.