Black symbolises the unknown, the subconscious, danger, mystery, darkness, death, mourning, rejection, hate or malice. The colour invites you to delve deeper in your subconscious in order to gain a better understanding of yourself. It also signifies a lack of love and lack of support. More positively, black represents potential and possibilities. It is like a clean or blank slate.
If the feeling in the dream is one of joy, then blackness could imply hidden spirituality and divine qualities.