How could one use the Gimp to easily transform a map with many colors into a map where each country is fully colored in a single unique color. I used the Color > Threshold option to get a b&w image, then filled the country-borders with more black pixels where they were missing, and erased the black pixels inside a country's territory, before using the fill tool to fill each country with its own color.
That's very tedious and long work, and probably someone has a better idea, which they'll be happy to share with me ;)