I think it would be a good idea to convert all the images done so far so that they can be put through the color switcher. This would have two important benefits- first, it would allow the same image to be used for different items. Second, it would allow the item images to be cleared from the cache when no longer in use. As of right now, images with palettes are cleared from memory if they haven't been used in a while, while images without palettes remain there forever once loaded.
To do this, one could load the image into GIMP, put the item image on its own layer, convert to monochrome, set the mode to Multiply, then apply the color beneath.