September 2, 2010 
People who are depressed actually see in gray color, as this condition causes changes in vision, German scientists established…
In fact, depression affects the eyes so it is difficult to spot the contrast of black and white so that everything blends into gray.
After the tests on the retina of patient, it was showed that the effect of depression is like the effect of turning off the contrast on your TV.
This could be the reason why artists in all times and all cultures consistently describe depression with symbols of darkness and drab grayness.
Taken from: www.jutarnji.hr