Aura, after-images and things like that.

Most of the time our vision works automatically, adjusting to changing light levels, colours and shapes and movement, without us noticing the complex task it is performing. But in certain situations so often we get a glimpse at the workings of our visual system:

• Bleaching takes place when you look at something bright - it takes a little while for the 'afterimage' to fade and vision return to normal.
• Look at an object of a bright colour for a while, and then at a white page, and you'll see an 'afterimage' in its complementary colour.
• Stare at an object of a bright colour against a blank background for a while, and because of the small movements the eye makes, this complementary colour afterimage will appear as an 'aura' at the edges of the object.