Okay so my boyfriends car (C300) was really dirty because he's been working like 70-80 hours a week lately and hasn't had the time/energy to clean it so I went to Home Depot, picked up car wash and Armor all because I thought that cleaned the rims. Well I clean the car and the center Mercedes icon on all 4 rims are like white and look corroded now!! Is there a way to save them? Would this have caused this or is it possible they were already like that? Picture below of the rim most affected

 

The center caps are replaceable... check price with dealer ... then you can check eBay:

https://www.ebay.com/b/Mercedes-Benz...961/bn_1441832

Since you are not "saving" the old one's - you can "pop" each one off from the front - don't scratch the wheels - and the new ones will easily pop back in.

 

Throw some dirt back on them and don't say a word...

 

Nothing in Armor All is corrosive or would cause oxidation like that. The center caps were likely in that condition previously. Do you live in a part of the country that uses road salt in the winter?