Open the image file menu Colors/Map/Color Exchange Press the colour selection for ""From Color"". Set R, G and B to all 255. Press OK button. Press the colour selection for ""To Color"". Set R and G to all 0. Set B to 255. Press OK button. Press OK button.
White and black are special... If you want to translate all other colours then:
Open the image file menu Colors/Hue-Saturation Press ""Master"" button Drag the Hue slider"
"The GIMP is what you want, but learning how to use it is far beyond the scope of this site.
There are innumerable tutorials for simple effects like this; I would suggest firing up your favorite search engine, and looking for ""photo retouching""."
