I have and now I'm going to show you how to do it yourself.
First open up GIMP. If you don't have GIMP, then get it from here.
Sorry the video is choppy and a little blurry.
Step 1: Open Up the Image in GIMP.
Now open up the image that you are going to use. My picture wasn't the best because I couldn't figure out where the rainbow was later on. So make sure you use an easy photo for the first time.
Step 2: Duplicate the Image.
Now in the Layers menu click the button that duplicates the image.
If your Layers menu isn't open:
1. Click File
2.Go to Dialogs
3. Click Layers
Or do Ctrl+L
Step 3: B&W
Now we need to make this image Black and White.
To do this:
1. Go to Colors
2. Click Colorify
3. Click the white box.
4. Click ok.
Step 4: Making the Color Detail.
Now you need to zoom in on the area where you will be making an item colored.
I decided on this rainbow picture, but I didn't know the rainbow would cause a problem.
Step 5: Use the Eraser Tool.
Now this is where the item that you picked to change into color will appear.
1. Choose the Eraser tool.
2. Color the area you want.
Once again, this is where the rainbow came to be a problem for me.
Step 6: Saving
Now all you need to do is save the image!!!
The File menu to save the picture is the picture window. Not the GIMP window.
Step 7: You're Done!!!
Now all you need to do is appreciate your picture.
Below is another picture I did that demonstrates this better.
Pictures: Courtesy of Google
ZoeE1 made it!