edit image in darktable (1)
export as 16 bit greyscale tif, import to gimp, image > mode > rgb
create new image, fill it with gradients including greyscale black to white, go to the palette menu, import palette from that, sort palette
go back to imported image, select newly created palette, colors > map > palette map
your greyscale image now has colors inserted into it based on an algorithm i dont fully undesrtand (2, 3).

came across this tool in my quest for introducing false color to a greyscale image to cover grey tones lost in the export to 8bit jpg from higher bit depth raws. this doesn't end up doing that, but it looks pretty cool