replacing colors exactly in gimp?

i’m making a weapon for a video game and there are 2 teams, red and blue. some weapons are red on red team and blue on blue team. some weapons have brush strokes on them to make them stand out more. but i need to know how to have all reds turn to blue exactly.

http://puu.sh/1TQjV

heres the red team version, but i also need a blue team version, so i use the color exchange tool to change both the base red and the brush stroke red, which is slightly darker than the base color.

http://puu.sh/1TQoN

as you can see, some of the areas are still red. i can always manually edit it to make them blue, but i need it to be perfect. i see people all the time making blue versions of red weapons and they are all red and blue without any difference in the texture besides the changed color. how do i change every red color to blue exactly and without any mistakes?

also sorry if this isnt the right site for this question. i cant find any other gimp support forum thats active.

colors->hue-saturation->fiddle w/hue

thanks. this helped a lot.