No need to worry. But yes it's the beginning of some infection as you are having complaint of mild pain and swelling. Need a x ray to see whether infection is in tooth or gums. But as I can see in attached photograph their is small cavity on  tooth also. So it's better to visit doctor online or offline for better treatment plan. You can apply gum paint over this part.

Hello There is no need to worry about it, or even biopsy at this stage. Getting a professional opinion along with a radiograph is imp right now regarding your pain n swelling According to the image uv shown here, looks like a small scale infection and pigmentation is a reaction to it. There are many factors causing pigmentation and the one causing ur pigmentation looks quite clear from the image, it can be due to a pocket or food lodgement. To attend that properly you need to visit a gum specialist (periodontist) asap because it is not a self healing lesion and may soon start bleeding while chewing or brushing or pocket depth may increase

Greetings, no need to worry. if you are experiencing pain and swelling then you can visit a dental clinic for a proper check-up and an x-ray of that particular tooth . Things will much clearer after a check up.