Okay for one of my first icon tutorial's
you'll learn how to turn this:

into this:

Start off with a 100x100 new layer and take the image you want to edit
1. First duplicate the base and set it to screen
2. Duplicate the base again and desaturate it (ctrl + shift + u)
3. Now take the eraser tool and erase the parts you want to be colored
4. Duplicate the base twice
5. Set the first one to Screen at 50% opacity
6. Set the second to overlay
Your layer palette should look like this
