iPhone X Space grey band discoloration

Hi,

Today, I brought out my X from casing to do some clean up, but I saw my 'mute switch' discoloration, being darker than other areas and has some blue/white tint (like a titanium). I tried wiping the blemish off, but doesn't work.

The blemish looks something like the picture below (got from a guy in Reddit)

Anyone happen to know what might have caused this? I tried everything but the tint is still there.

And can I get a replacement from apple?

Please help.