They are either chromed or galvanized steel. Since you say "whitish" I'm guessing they are galvanized. Painting them is not a good idea and wouldn't last long if you did. I suggest going to an auto parts store near you and picking up a can of a product called "Nev'r Dull". Cost about $4. It's in a silver can about 3 inches in diameter and about 4 inches tall. It's a wadding compound for removing oxidation and for polishing. Pick up some shop rags while you are there, too. I buy the cheap-o bag of red rags. Tear off a little piece of the Nev'r Dull and spend about 5-6 seconds rubbing it up and down on a spoke in a quick repetitive way. Then take the rag and rub it down the same way for a few seconds. It should remove most of the oxidation, and if you're really lucky that spoke might also be shiny. Keep going until it's all to your liking.

Karl