Gray/grey is the color that has had the connotations of depression, boredom, neutrality, undefinedness, old age, contentment and speed. It is perceived as safe, long lasting and classic. It is a color that carries authority and dignity. It is reliable, mature and practical. Gray is controlled and almost imperceptible. It's a perfect neutral color and is seen as a color of compromise, perhaps because it is between the extremes of white and black.
Grey is used in ethics to describe a moral situation of no clear disposition, or, as in "shades of grey", to dignify levels of integrity. Similarly, the term "grey area" is used to illustrate a philosophical concept that one is unable to place.
Grey is also often commonly associated with the elderly or aging, as hair loses its pigmentation from passage of time.The Bible used gray to signify old age.
In the area of parapsychology, those who are believed to be suffering from clinical depression reportedly have grey auras. Interestingly, to be "grey" is French slang for inebriation.