You know thats a good question, i dont think it would, as long as you dont spill paint on the inside. Basically when I have talked to techs about self installation, they say warranty remains as long as you dont screw anything up. This is a different scenarion though, but I would guess the same thing would apply. If something did screw up, you could argue it to the death, ya know like whats the difference between putting a sticker and some paint, it doesnt affect the internals at all. Like picard said though, it would be much safer to get a quicksnap. But if I had the equipment and the know how I would paint mine.
