This is an edited version of the original "color replacer" effect, modified to be able to replace up to 16 user-defined colors.
Basically, it takes a user-defined color and replaces it by another user-defined color. I've made this so I can have multiple palettes in my game without having to edit the graphics.
I've also included 2 examples: a "palette generator", which you can use to edit your own 16 color palette and save the output to use in your game, and a simple example that loads up a palette.
Edit (fixed link)