Color Count

Color Count is a Paint.net plugin that gives you the possibility to count the total colors within your photo project. It contains approachable configuration settings that can be figured out not only by experts users, but also by those less experienced with this advanced image editor.

Simple integration with Paint.net

In order to get this extension up and running, all you have to do is copy the downloaded DLL file to the "Effects" folder of Paint.net's installed directory, restart the application if it was already launched, as well as start the new plugin from the "Photo" submenu of the "Effects" menu.
This also works if you have a portable edition of the program at hand. The add-on should be easy to spot in the menu, since it's marked with a tiny icon that looks like a puzzle piece, which is available for all external extensions.

Easily count image colors

Color Count doesn't have a built-in color picker, so you have to resort to Paint.net's tool dedicated to this task, in order to select the primary and alternate color from the loaded graphic file.
The add-on can be asked to count both primary and alternate colors, or only the primary one. It can optionally ignore alpha and transparency variations.
In order to obtain the color count, it's only necessary to click a button. This value can be selected and copied to the Clipboard by triggering the global hotkey or by opening the right-click menu.

Evaluation and conclusion

Although it hasn't received updates for a long time, it successfully integrated with the most recent version of Paint.net in our tests, without causing it to hang, crash or indicate errors.
To sum it up, Color Count offers a simple solution for swiftly finding out the total colors within photographs.