Nocturne also does this. I keep it for inverting my Menu Bar when not in use. It would be of course more convenient if f.lux would do this so I can get rid of one extra app in the menu bar.

http://github.com/InBeta/nocturne http://www.blacktree.com/projects/nocturne.html http://code.google.com/p/blacktree-nocturne/downloads/list