A dream in which you see or eat blackberries means that you are acting without caution. It is also symbolic of repressed carnal urges.
To see a dream in black and white indicates your need for more decisive and clear action. Your subconscious is instructing you to conduct your waking life with more purpose and clarity and eliminate excessive gray areas.
Alternatively, noticing that you are dreaming in black and white and that your dream is rather dull, it may be your subconscious suggesting you to add more excitement or 'color' to your waking life.