My guess would to pry between the side "buttons" and the top shell. I'm guessing this since if you look closely when you click the mouse, the entire outer shell moves but the side 'buttons' don't. The side 'buttons' are connected to the bottom part of the mouse. I think if you find out how to pry off that white outer ring on the bottom that goes around each 'button', it looks like you could then just pull the top outer shell off, and then paint it.