Saxophones are made of brass, and brass is made of copper (among other metals). Copper in the brass oxidizes causing the green spots. This is like rust on steel. You cannot simply clean it off. To remove this you need to have it chemicaly cleaned, or put in an ultrasonic cleaner which shakes all the corosion off leaving you with shiny brass again. Do not try this yourself, and consult your trusted tech before having them do it. Some older horns cannot handle the cleaning processes and will lose laquer as a result. If you play on a bundy, it is not really worth having the corosion cleaned, unless it is close to your heart. The corosion is a visual issue mostly, but after many years will cause pitting and eventually a hole in the horn, but that takes a few years, unless you frequently play in the ocean or some other large body of salt water. Hope this helped.