Black Mattress in dreams
The base of the bed — the thing your whole weight is given to every night.
How black changes the reading
Black colour pulls the symbol toward the not-yet-known — depth, hiddenness, the part of the situation that has not yet come into the light. The dream is rarely warning you; it is showing you that there is more to the picture than the part you have been looking at.
The base reading of Mattress
A mattress in a dream is the dream's image of the structure that holds the entire weight of you while you are not guarding yourself. The dream uses it to talk about the base support of your life — the relationship, the home, the body — that takes your unconscious weight night after night without applause. A firm, intact mattress is the dream affirming that the base is good. A sagging, stained, or broken mattress is the dream noting that the foundation you have been collapsing onto is itself failing, and your sleep is telling you so before your waking mind has caught up.