How do I get the white rubber on the side of my shoes to go back to being white?

I have an older pair or shoes in good condition that I forgot about while moving. When I found them, the white rubber along the sides (like converse) has turned this dingy cream color. When I got them, the rubber was white. I've tried using vinegar, bleach, and other house hold cleaners that might be more powerful. Is there a product or some trick I can use to get my shoes looking good again?