I have here with me a book called "Fiat 500 - la guida/the guide" and for the wheels it says: "On the new 500 Standart(nuova 500 economica) rims are mounteed with welded cap, painted in cream color, without any aluminium cap." And there is a black and white pic that looks like the rims in the pic that you show.
I hope I could help you.