Depression actually alters vision, making the world appear far more dull and monochrome. This is due to lower Retinal activity in comparison to someone that doesn’t suffer from Depression.

How depression makes the world seem gray, from the Harvard Mental Health Letter

Depression is often referred to as “the blues.” New research suggests it should actually be called “the grays.”

To someone who is depressed, the world can seem flat or dull. This was long thought to be purely psychological. It turns out, though, that depression may affect how the eyes function—altering visual perception in a way that actually makes the world look gray, reports the November 2010 issue of the Harvard Mental Health Letter.

Source: https://www.health.harvard.edu/press_releases/how-depression-makes-the-world-seem-gray