For all you who might be looking for a application which can count the number of UNIQUE colors used in ANY image file, please find the link below.

Completely open source, direct link to mediafire.
Just though someone might want to use this.
Coded it over lunch.

Tested it somewhat. Seems to be very(!) accurate.

Hope you like it. (C# source included and zipped with 7zip, no password protection)

DL Link: http://www.mediafire.com/?hqhe8xo4tg4mx1p

Enjoy.
Feedback non-essential, but will accept it along with critique.

Cheers.

O.