Any paint program that has RGB coloring can be used to re-color you fractal. However, doing this will remove the GIF89a info fractint needs to reload/redraw your fractal and the result will be a plasma. There is a workaround if you want to do it. Make a copy of the original saved GIF and use the copy as a work copy for the new palette. Then load the work copy back into fractint and color cycle your new plasma. While in color cycling enter <s> and save the map. Then use the saved map to recolor your original fractal.