If you have some older E2 or Sig Pro sandpaper type grips, you know they eventually turn brown down inside the texture. It's not dirt but simply the polymer changing color with age. I've tried all kinds of things from simple soap and water to Armor All and tire shine without success. I keep a small tube of black acrylic paint in my shop so I decided to "paint" the grips. I placed a few drops on each area and rubbed it in good with an old toothbrush. I then rub off all the excess with a clean white cloth. The grips then look like brand new again. I've done this on several grips and the color does not come off after several months of use. I've also used white acrylic to refresh the white dots on my contrast sights and they too have held up well even with the various cleaners that I use on the gun. This should also work on some of the other models like the 320 and 365. FWIW