There's a black layer around my piercing?

so I've had my piercing for a week now and I clean it with saltwater twice a day, as I was told. For the first 2 days there was dry blood around the piercing (barely visible though) but now I noticed there is something black around, what could it be? Also can you please tell me for how long do I have to clean it with saltwater and when can I take the stud off?