seeing the "what's old is new again" thread brought up a question i have been meaning to ask for quite a while now, but i always forget to ask..............

what color of paint, or what technique could be used, to replicate the greenish/gray color magnesium wheels turn to, when they are not kept up ?
i have read a couple of articles on how to duplicate the Dow [? number] coating that was the yellowish coating applied to new wheels, but never anything on how to make wheels look like they would get if left to the elements.
flat black doesn't get it, even though "flat black" from spray bombs of different companies often are different shades.
any suggestions ?
a BIG TIA to you guys who are way smarter than me.