if you have or can get a polishing wheel, have a go at it with that! not sure how well it will work out for you, you have heated the metal to it's discolor temp, they may never come back! if you want to try and hide it and give your bike a bit of a race look you can go header wrap, or you can pull it off and send it to be coated, or paint them yourself! the coating or the wrap may help you run a bit cooler, they are suposed to hold the heat inside the pipe, keeping the air flowing over the motor cooler! i think the header wrap would keep more heat in in than the coating!