It is hard for me to know without seeing him, but what you are describing sounds like totally normal pigment (freckles) that many cats are born with.
We can see black areas on the gums normally. If they are raised bumps then I would want to check them, but if they are smooth and flat, just like a freckle on your arm, then they are almost certainly normal mouth freckles on your cat!
We see this more in cats that have black in their coat, but it can be in any cat.
I hope that this answers your question!
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.