Back cover discoloration

[vilwen]

 i got this phone a month back. I'm not sure if this discoloration is wear or just some kind of "paint" from my trousers pockets. 

According to a post on Reddit. Everybody out of 5-6 people still have mint condition back covers.

Anybody have a way to perhaps restore the back cover?

[vilwen]

So that means the black and blue are made from the same material?

Discoloring something black is usually a bit harde ;).

Yeah of course the people on Reddit did not specify color.

[vilwen]

Yeah not rusty. More greyish, imagine pocketlint color.

[vilwen]

Only the edges of the cover.

No it is that bad :(. Brownish/greyish as in the picture

[vilwen]

@Mansi_ASUS 

Do you have any suggestion for this issue?