Grey
Ambiguity — neither one thing nor the other, sometimes resting state, sometimes flatness.
Grey in a dream is the dictionary's image of ambiguity. The dream often appears in stretches of life that have stopped having a clear emotional colour — sometimes a resting phase, sometimes a phase that has flattened in a way that needs attention.
Where you often see it. A grey street in early morning. Grey sky before a decision. Grey clothing on a figure whose role is not yet defined. The dream uses grey for the in-between — neither one thing nor the other.
What it is not. Grey is not flatness or depression by default. Often it is the dream signalling a resting state in which decisions are not required.
Related in the dictionary. Read grey with fog (loss of clarity), winter (still phase), and silence (what is not yet being said).