Gimp Tool of The Day: Rotate Colors

I needed to convert an icon from one color to another^*. I couldn't use the simple bucket fill tool The Gimp has (at least, I don't think I can) because the icon contained a variety of shades of color.

A little poking around The Gimp manual brought me to Rotate Colors. Here's the screen that pops up when you select that option:

Turns out to be a pretty intuitive UI - I just dragged around the various selectors until I had the color substitutions I needed. Here's the finished product :

Have to say, The Gimp saves the day again. This can't be the only way to get this effect - what other ways are there to do this?

Thanks to freeiconsweb.com for providing a sample icon I could plug into this example.