This is a GIMP script, written in python.
See the following address to install the script:
https://en.wikibooks.org/wiki/GIMP/Installing_Plugins#Copying_the_plugin_to_the_GIMP_plugin_directory

When installed, the script will be listed under the "Colors" menu.

It requires a relatively recent version of GIMP. 2.6 is too old.
