Dream interpretation is extremely subjective. Here is one interpretation of "black" and "dog" from
http://www.dreammoods.com/:
Black symbolizes the unknown, unconscious, danger, mystery, darkness, death, mourning, hate or malice.
If the feeling in the dream is one of joy, blackness could imply hidden spirituality and divine qualities.
To see a
dog in your dream indicates a skill that you have ignored or forgotten, but needs to be activated. Alternatively, dogs may symbolize intuition, loyalty, generosity, protection, and fidelity. Your own values and intentions will enable you to go forward in the world and succeed. If the dog is vicious and/or growling, then it signifies some inner conflict within yourself. It may indicate betrayal and untrustworthiness. If the dog is dead or dying, then it indicates a loss of a good friend. Alternatively, it represents a deterioration of your instincts.
To see a happily barking dog in your dream, symbolizes pleasures and much social activity. If the dog is barking ferociously, then it represents your habit of making demands on people and controlling situations around you. It could also mean unfriendly companions.
To dream that you are buying a dog, indicates your tendency to buy your friends or buy compliments/favors. Alternatively, it suggest a need for you to find companionship.
To dream that you are dressing up your dog, signifies your attempts to cover up your own character flaws and habits.
Also consider the notions associated with the word dog, such as loyalty ("man's best friend") and to be "treated like a dog".