Use a grease cutting hand cleaner (liquid) or a grease cutting dish detergent. Put a little right on the stain, soak it in cold water for 1/2 hour, add more grease cutter soap to the stain and wash...
I have personally only been able to get the stains out by just using them and washing them. I guess after repeated usage and washing it has faded away...I have however found a way to keep the tomato...