Our eyes are made up of two types of cells: rod cells, which are primarily responsible for perceiving light, and cone cells, which handle color.
There are three types of cones — ones that handle green wavelengths of light, ones that handle blue and ones that handle red. If you overstimulate one type of cone by flooding your vision with a bunch of that color, those cones will become temporarily unresponsive.
As a result, your eyes are forced to rely on the other two types of cones, which will show you only the opposite “complementary” color (ex: if you flood your eyes with a bunch of green light, the other two cones will show you red). This reaction can be used to “trick” your brain into perceiving colors that aren’t actually there.
In the new BBC Four series “Colour: The Spectrum of Science“, host Helen Czerski got to try out the method for herself. Check it out in the video below to see if you can trick your brain into colorizing a black and white photo:
(h/t IFL Science)