Black mold inside Misto oil sprayer collar

What you are seeing is almost certainly a form of firescale, and it should be completely harmless. If the discoloration bothers you, you can try to remove it using the aforementioned Barkeeper's friend or a mixture of boric acid and denatured alcohol (which are non-toxic).

With regard to cooling off the pan, you should never put a hot, empty pan into a cold, wet sink: The temperature change can cause the pan to warp.

Black mold, regardless of what type it is, is not good news. It is almost always introduced by contact with contaminated skin. Your best bet is to trim the outside one inch from the entire cheese, ensuring that your hands are covered with latex or nitrile gloves that have been disinfected with bleach and then allowed to air-dry. Between each cut, clean and sterilize your knife to ensure that there is no chance of contamination by spores picked up during the previous cut. Re-salt to create a new rind, or apply some wax as a sterile seal. Ensure that the location in which you age your cheese is completely sterile before setting any cheese on it again, and do not re-use any cloths or paper wraps you may have employed before, even if they were used on a different cheese. If the black mold regrows after you have taken all of these measures and precautions, it means that there are spores in the cheese itself. If that is the case, I would recommend that you discard the cheese and start again.