This plug-in recolors the image using colors from the active palette that you choose in Dialogs → Palettes.

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.

You can access this filter in the image window menu under Colors → Map → Palette Map.