Positive: Psychological neutrality.
Negative: Lack of confidence, dampness, depression, hibernation, lack of energy.
Pure grey is the only colour that has no direct psychological properties. It is, however, quite suppressive. A virtual absence of colour is depressing and when the world turns grey we are instinctively conditioned to draw in and prepare for hibernation. Unless the precise tone is right, grey has a dampening effect on other colours used with it. Heavy use of grey usually indicates a lack of confidence and fear of exposure. 
