Start with Windex and keep getting more aggressive until it cleans up.

You can use 0000 steel wool with your cleaner - hell, you can use 600 Wet or Dry sandpaper with the cleaner if you need to.

I always clean my lenses with Windex first to remove the majority of the gunk on them. Then I get serious.

Remember, the color is actually part of the glass now. Unless you get crazy with the pressure, you can hardly remove well fired color short of sandblasting.

Jim