How to clean my white plastic iPhone case?

I ordered an otterbox defender series case for my 4s and when I got it I noticed the plastic part was a little off white… It looks a bit lavender. I ordered it off of amazon and I checked again and it said gunmetal grey/white, so I'm pretty sure I didn't order the wrong thing. I was wondering what would be the safest and most effective method to get the plastic part to be white

You can't. I had something similar wrong with an otterbox I ordered for my sons iPod touch. Once the color goes, it never comes back. Sorry