So your mask is stained right?
Pick up a bottle of Clean & Clear Oil-Free Continuous Control ACNE WASH
Its in a little purple bottle with a clear cap. It may make your mask smell girly but trust me it works.
I had a white EPS JT frame that had a overall pink tinge to it. After applying this stuff, it became white again!
Heres how to do it:
Take out lens, strap, ears, etc. until the frame is bare
Apply foam in bottle to every surface on your frame
Wait for 2 hours, or until foam dries COMPLETELY
Rinse with cold water
Let dry overnight
ITs that simple. Sorry I didnt have my camera for pics but trust me it works. You can get the spray at a local drug store for a couple bucks. If it cam work for me it can definitely work for you.
TRY IT OUT!