Different Display Themes/ Inverted Colors only on the External Monitor?

Is there any way one can invert colors only on the external display (or vice versa), an application (preferably for Snow Leopard, but later OS would be ok as well) with which one can do this? "Nocturne" was a great program allowing for the use of different themes on a single monitor or, with a second display attached, on the main and external monitor simultaneously. Maybe there is now an app that enables one to choose different display themes/ invert colors etc. separately for each monitor?

Thanks for any suggestion...

Ok, replying to my own question in case anybody else would like to do the same:

The answer is here.

More specifically, I tried the application Black Light on Snow Leopard and it indeed does just what I asked for above: inverting the colors on one screen while leaving the other one intact.