Things You'll Need
Instructions
Remove the Gameboy's outer case. If your Gameboy has three-headed screws, use the flathead screwdriver sized for eyeglasses. Bending the screwdriver will make this easier.
Loosen the screws that hold the electronic components to the outer case. There will also be a connector that goes from the motherboard to the LCD screen. This can be detached by removing a few pins.
Tape up the entire LCD screen so you won't spill paint on it, which could render the Gameboy useless.
Paint the case to your heart's content.