Testors spray paint does not eat foam, at least the flat black doesn\'t. There\'s also a brand here in the US called MasterCraft (I believe, that\'s it, I\'ll look tonight) that you can get in craft stores that doesn\'t eat the foam either.
I\'ve also heard that Krylons new Fusion spray paint doesn\'t either but I\'ve not had the chance to find out myself yet.