Your eyes have a history.
Vision adapts to sustained stimulation. After looking steadily at a coloured shape, a pale neutral surface can briefly seem to carry a differently coloured echo.
This is a negative afterimage. The visual system produces the impression; the page does not paint a secret complementary shape. Its appearance and duration vary between viewers and viewing conditions.
A colour that isn’t there.
Start the 15-second study and look gently at the central cross. The colour will disappear onto a neutral field. Keep looking: do you notice an echo? Stop whenever you wish.
Ready when you are. There is no flashing or automatic repeat.
What is really on the screen? +
During observation the page shows a teal disc. Afterwards the disc is removed, leaving only the neutral background and fixation cross. Any coloured echo is your perceptual response, not an animation. The effect may be subtle or absent. Use a comfortable screen brightness; you can read the explanation without doing the study.
Seeing is an active process.
An afterimage concerns a lingering response after a stimulus changes. Colour constancy concerns relative stability across changes of illumination. They are related topics in adaptation, not interchangeable names for one effect.
Follow the
colour further.
The ideas behind this volume.