Menzerna 7.5 Wheel and Tyre Gel,
It's pretty good stuff if you don't fancy using a heavy duty product such as Meg's Wheel Brightner. Spray it on and let it settle onto the wheels for 5-10 minutes, rub it in.. paying extra attension to the marks on your wheels. Leave to soak for another 5-10 minutes and wash off.
I use this on my superleggra's, granted there not white though.
If you don't wish to purchase a new product and you have some clay bar laying around give that a go. Clay bar usually removes any contaminates firmlly bonded on the surface of paintwork.
A good wheel sealent would help you with future washing, as an example Poorboy's Wheel Sealent. The more layers you add the more it helps repel brake dust.. makes cleaning the wheels a breeze. I also use this and when I come to clean my wheels all it takes is an old wash mitt to wipe them down.