The dark grey colour perceived by the eyes in the complete absence of light — not true black, but a uniform luminous grey caused by spontaneous neural activity.

Results from the random firing of retinal cells and visual cortex neurons even without any light stimulus, sometimes called visual noise.

Also known as brain grey, dark light, or intrinsic light — distinct from afterimages, which are caused by prior exposure to bright stimuli.

The German word combines eigen (own, intrinsic) with grau (grey), giving the sense of a grey that is native to and generated by the observer's own visual system.

Carl Jung borrowed the term in his analytical psychology to describe the grey undifferentiated state of the unconscious before archetypes take form.