I looked for it and the closest things I can find are the "Darkness" tile and the ones named "Hole (Stone Floor)", "Hole (Dirt Cave)" and stuff like that...I was using the dirt cave one, and I also realized I was using the dark ground tile and not the ceiling tile -- the problem is just that the dirt-cave-hole tile is apparently designed for the regular ground tile, not the dark one, which is a bit annoying. >_>
I guess I'll just go ahead and redo the floor with the lighter tiles, darken the screen and see if that looks better to me. Thanks a bunch for the help and suggestions, Dyluck!!