The purple on the aluminum rims is caused by dye that was applied during the application of the protective anodizing treatment. I believe that if you remove the purple, you will have removed most of the corrosion resistant anodizing also. (FYI Aluminum naturally forms an oxide coating when it is exposed to air. The oxide has good corrosion resistance. Anodizing greatly enhances that oxide and also hardens the surface to improve its scratch resistance.) I think even the aluminum colored rims have a clear anodizing.
Some possiblities: Lightly sand (600 grit) and then polish the rims and see how it goes. I wouldn't go near salt water and stay out of barnyards. Salt, ammonia (urine) and other waste products can wreak even anodized aluminum.
Polish them and have someone anodize them. But this requires removing the spokes and relacing the wheel. Doable, but time consuming.
Replace the rims with new or used ones of the color you want; black, gold, aluminum. (I have a bent gold 21". I don't think you can straighten it. It is out of round and out of plane.)
Good Luck. I hope you can get rid of those ....what should I call them? not faggy, nor femmy, maybe Frenchy?...just ugly, purple rims. Thanks for trying to improve our environment.