You can find this filter through
-> -> .
This plug-in calculates the most often used color in a specified border
of the the active layer or selection, allowing a specified range to not
be exact. The calculated color becomes the foreground color in the
Toolbox. This filter is interesting when you have to find a Web page
color background that differs as little as possible from your image
border. The action of this filter is not registered in Undo History
and can't be deleted with Ctrl+Z.