This plug-in recolors the image using colors from the active palette
that you choose in
It maps the contents of the specified drawable (layer, selection...)
with the active palette. It calculates luminosity of each pixel and
replaces the pixel by the palette sample at the corresponding index. A
complete black pixel becomes the lowest palette entry, and complete
white becomes the highest. Works on both Grayscale and RGB image
with/without alpha channel.