Grey Mattress in dreams
The base of the bed — the thing your whole weight is given to every night.
How grey changes the reading
Grey colour layers ambiguity onto the symbol. The base meaning is still there, but the dream is saying you do not yet have the colour information — the situation has not declared itself.
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.