How to do multi color prints with one extruder
Getting a multi colored print with one extruder isn't that difficult. You could go and buy e3d's cyclops, but it will require an additional extruder/stepper motor. The easiest way to acheive a multi-color print is by changing out the filament at different heights.
One way of doing this is by watching the print and cutting the filament at the desired layer you want to color and feeding the extruder manually with the next color to use. This is pretty tedious, but if it's a small and quick print, it won't be so bad. Also it's good practice when you notice your printer is running out of filament.
The next and best method is to edit the gcode file at the layer height to pause so you can switch filaments. I wrote up about this technique a while back.