I recommend you learn to live with it. The aluminum is anodized, meaning it has been electro-chemically processed on an industrial basis to create a protective clear layer of aluminum oxide over rhe bare aluminum. There are no after-market "patch kits" possible that can re-anodize the case after manufacture.
Attempts to clean/ scrub/polish it will make it far, far worse.
We've seen this here before. Apparently some sticker adhesives can act on the anodizing and cause discoloration.
The only fix is to replace the display case if it is a non-Retina Macbook Pro, or the entire display assembly if a Retina model. The latter repair will make a US$500-600 hole in your wallet— your cannot just replace sub-assemblies in a Retina display