Were they painted silver and black?, or was the 'silver' actually diamond cut?. If so, you won't easily be able to replicate the finish, but either way, I think it highly doubtful rubbing the wheels with a petrol covered rag would remove the paint you put on, but not damage the original finish underneath (given you sanded them).

What kind of car and value are we talking about?, because a slap dash paint job on the wheels will affect the value and saleability of a decent car. Might be better to get them done by a pro, or get 2nd hand or aftermarket alloys if it is.

Petrol will not do anything, it's a poor solvent. White spirit might do a little. Try Nitromors cautiously on an inconspicuous area.

Sunlight works.

Nearly all the top colour has gone from my roof and bonnet, leaving just the grey primer, apart from a little bit of red in the radio aerial shadow.

Might take a while in The Yook though.

Brake fluid would probably work too but I suspect it might go through more than 1 layer at a time.