a scanner darkly

The colour background that one sees when one closes one’s eyes is called Eigengrau (German for intrinsically gray) and is brighter than what we perceive as the blackest black because there’s no contrast behind our eyelids.
The term was coined by experimental psychologist Gustav Theodor Fechner in the 1860s while working at the University of Leipzig whilst studying the relationship between sensation and perception, famously recognising that not everyone will see the same colours as demonstrated by contemporary and toy-maker Charles Benham with his top. Just as the Eigengrau that people report is hard to measure and is subjective, the subtle arcs of colour (called Fechner colours or flicker colours) are not the same for every observer—and no one can quite say why. The flashing image might make some people dizzy, so click here to view it. What colour are the tracers that you see? Is it the same for this one (caution flashing images) too?