Looks like an aluminum Moka pot, the only thing that I know that causes that oxidation and or corrosion is washing it in a dishwasher which the acid in dishwasher soap ruined the protective coating on the aluminum allowing it to oxidize. My Moka pot company said never to use any soap to wash the pot, nor use any harsh cleaning brushes!
Why is that? because aluminium is sort of like cast iron, you have to season cast iron, and an aluminum moka pot has to remain seasoned with coffee oil, and the oil also seals the aluminum to keep the metallic flavor from leaching out into the coffee, that means you should never get the coffee stain out because that's the oil and that oil is necessary to impart richer coffee flavor back into the coffee. So all you do to clean it every time you use is to simply use cold water and a soft cloth.
Americans don't like the idea of something looking dirty, and the insides of a well used aluminum Moka pot will look nasty after time, but that nastiness is the coffee oil which is good for the coffee flavor. But if you don't like your Moka pot to look like that then I suggest getting a stainless steel Moka pot, those you can throw in the dishwasher and be done with it, but you will never get that true strong rich Italian moka coffee flavor due to the stainless steel cannot hold onto the oil. Stainless steel is not the Italian norm, the only reason why stainless steel moka pots are made is because of Americans wanting to keep things clean looking.
If you don't use a aluminum Moka pot every day the oil can go rancid after it sets for awhile then you may have to use hot water and a rag, or even just your thumb to get much of the oil off. The only thing on a Moka pot that requires washing by hand with soap is the O ring. If you have to use hot water and a rag or your thumb for cleaning then it's recommended that you run a throw out batch of coffee for it's initial use after such cleaning.
If you buy a new Aluminum Moka Pot you need to run 3 things of coffee through it and dump it each time to help the oil to seal and season the Moka pot before drinking coffee from it the first time.
Also keep on hand a couple of O rings, because once the O ring goes bad so does the coffee!