How to get overspray off tires

So, when I bought my Dart I kicked $300 off the dude's asking price simply because he made an attempt at painting the wheels on only one side of the car white. It's not even white though, it's grey. Anyway, one side of the car has really nice fire-engine red wheels, and the other side has grey wheels with overspray all over the tires. I can deal with the grey wheels, but how do I get rid of the grey tires? I have tried wiping it off to no avail, and do not really want to scrub at it for fear of scratching up the tires, so... help?