Colour in the Absence of Light
When you close your eyes in a perfectly dark place, be it a lightproof photo development room, a deep cavern, or just beneath a snug-fitting sleep mask, you won’t, counter-intuitively, see inky pitch-black darkness.
Instead, you’ll perceive a very faint grey colour known as “eigengrau”. Why do you see any colour at all, and why the odd name?
What is the name of the colour that our eyes see in the absence of light?
We don’t see perfect darkness even when there are no photons entering our eyes because of a particular protein called rhodopsin in our retinas. This protein, a component of the retina’s rods, is extremely light-sensitive and helps us see even in very low light conditions.
When we experience a dark grey colour in the absence of any actual light, what we’re actually experiencing is the thermal isomerization of rhodopsin (a process where heat triggers a chemical reaction that causes a molecule to reform into a new and different molecular structure but still have the same atoms).
This process triggers false positives in the rods and creates the illusion of faint light hitting the retina. When you see this faint grey behind your eyelids as you’re drifting off to sleep in a pitch-black room, what you’re really seeing is the side effect of biochemistry playing out across your retina.
As for the name, “eigengrau”, it’s derived from German and literally translates as “own grey”—a fitting term for a faint grey colour specific to the biochemical processes in our eyes.