The world does not literally become black and white, but nothing in the world is capable of engaging the mind enough to elicit even the briefest saccade and fixation upon it. Attention must be forced upon objects in the world, laboriously and painfully, and the entire perceptual experience is dull and muted, as if the internal emotional pain has become so overwhelming that it has cast a grey fog over the landscape.
The symptoms are profoundly physical; physiological in nature. It is without doubt a disease of the physical body; albeit one which often seems driven by a fractured and injured psyche throwing out discordant, disordered and malign thoughts.
Recovery from depression feels like waking up. The blinkers withdraw, and the world expands, becoming larger, richer and more engaging. The brilliant yellow of a flower is quantitatively still the same, yet draws the eye and becomes an occasion for delight whereas before there would have been nothing.
This experience makes the most sense for me when I consider perception as an active process. Information does not simply fall into the eyes to be passively consumed. Our perceptual experience is a dynamic thing - a continual act of the imagination, only just held in check by our senses. Depression distorts and undermines that part of our imagination which we use to see the world.