The hardest part of depression for me is that it makes me feel cold. Not physically cold, but inside, on an emotional, spiritual level. When I'm having a down day, my soul feels cold. It's taken me a long time to find the words to describe how I've been feeling. The world is a little less colourful and bright; the saturation's fallen out. Again, this isn't a literal vision problem, it's this feeling of cold.
Inside, sometimes it's a gloomy, bleak winter's day where the heating just isn't keeping up now that the sun's slipped below the mountain, and the fog is getting almost blue in its dimness.