Well, the noun "jankes" (plural "jankesi") exists, it's hard for me to say, but I think it has slightly negative connotations. "gringo" would probably be understood, but I don't see a reason for it to be said naturally by a Polish person, we're kinda gringos as well, right? ;) Unless gringo really has to be from an English-speaking country. I don't think there are other words, unless they're even more colloquial.
Well the original and most widely use for 'gringo' is to refer especifically to a person from the USA, regardless of physical appearance. However, in the less educated portions of Latin American countries, anyone resembling what they consider a gringo to look like (blond, light coloured eyes, white skin) would be called a gringo. Sometimes even locals are called "gringo". ;)