Black is a formal and conventional non-color, as opposed to green, which is the color of life. Usually, it is used to symbolize death and mourning, but there are countries that use white for the death ritual, like the Chinese. Therefore, black as a dominant 'color' in one's dream may bear a negative significance and can be the reflection of an annoying situation or grief period one experiences in the waking life. Or, it may also foretell bad luck and unhappy events to follow in one's life.
If we see black as associated with darkness, then it stands as a metaphor for the shadowy realm of human subconscious, where we bury all repressed feelings, emotions, anxieties, fears and unsolved conflicts. Consequently, dreams of black may be taken as an advice to release all negative energy inside, as this is a mandatory condition for achieving an emotional balance and general equilibrium in the waking life. Do not run from what you feel, instead find the power to face all that is eating you up inside, all the suppressed anger and aching accumulated within your soul.
Black in dreams may also represent one's low self-esteem, lack of self-confidence and even tendency towards victimization. Also, forewarns health disorders one may develop, bad luck and failure one may experience in undertakings etc. In conclusion, black is generally a bad dream omen.