Easily map colours from a source colour to a target colour. Very effective for matching skin tones across images or between people.
Relatively quick (but not earth shattering). It doesn't work with grayscale or indexed images. Has preview, works with selections and layers, etc. Very, easy to use, and quite useful for portraits or recolouring graphics.
A demonstration: Lenna's face is mapped to the colour of the feather on her hat. This was done by selecting a colour from her face, then selecting a colour from the feather.
If you have an x86_64 version of GIMP 2.7 on linux, bunzip2 and move the colour-match file to your plugin directory:
chmod 700 colour-match (Make it executable)
mv colour-match ~/.gimp-2.7/plug-ins/colour-match
To build it type:
gimptool-2.0 --install colour-match.c
You will need libgimp-dev, and libgtk2.0-dev packages if you didn't build GIMP from source.
The algorithm is based on the relative color remap plug-in by Lars Clausen ( http://registry.gimp.org/node/5442 ).