(http://i.imgur.com/D1pjOGF.png)
(http://i.imgur.com/1FM7vz3.png)
On the other hand I've never seen darker tiles against a lighter background so it might be interesting.
On the other hand I've never seen darker tiles against a lighter background so it might be interesting.
The background of the L2 shadow tileset does exactly this.
(http://i.imgur.com/lVohdVE.png)
However, with the new NeoLemmix v1.47 update, the trigger area of the exit has gone off by a lot of pixels (as seen in the picture below), and the lemmings are no longer able to exit. You may need to fix up the trigger areas of all the objects.