I think the wheels you have are one of the best designs in the range. The ride on 15" wheels is also better than on 16's. You could get them painted white.
Personally I'd leave it as it is... If you paint the wheels and fit white mirror caps it will look like a colour therapy model.
Too much white may also make the cream roof look out of place.
Have you got 'fiat' valve caps fitted? : P