Not too hard, unless you wish to paint the tray as well. if the case aesthetics is all you need its fairly simple. Use vinyl dye to do it- rather than paint the surface, it adheres to teh plastic and soaks into it, giving it a very clean look. It can be found at auto parts stores in the paint section.
First, take off the face of the drive (the little "door" attatched to the tray). Most drives just require you to tug out from the bottom, then up to slide the face off.
Make sure there are no screws towards the front of your drives that hold on the front bezel, then use a flathead screwdriver to (gently) depress the four (maybe six) latches that hold the bezel on.
From there its easy sailing! Make short thin coats in a well ventilated area and youll end up with positive results. much like my old case: