Let’s begin with an activity…

Stare at the pink dot on The Think Tank while you count to 10. Then look at the pink dot on the right and count to 3 while letting your eyes blur slightly.

Did you see a strange image of a ghostly pink Tank topped with a glowing green brain? If so, that’s a color afterimage. Keep reading to learn more about “color opponency”, the mechanism behind the pink Tank and similar afterimages…

When The Think Tank takes science to the streets, we show people that they have the power to change their own brains and minds. A favorite children’s book shows just how fast we can change them. Renowned author Eric Carle introduced many children to the curious case of color afterimages through Hello, Red Fox – a strange title if you do not consider the psychological concept at the center of the story.

So color afterimages are fascinating, and they have been popularized by a children’s book author, but why do they happen? To answer that question, we must journey deep inside the human eye to a region called the retina. That is where light from the world enters and information about it – including its color - is sent to the brain. When light reaches the retina, it interacts with special light-detecting cells called photoreceptors. Most importantly for color afterimages, the retina is lined with rows of cones, which are special photoreceptors that detect color.

When scientists studied the cones more closely, they discovered that the explanation for color afterimages specifically rested in their organization. They found the cones arranged in pairs, with each member of the pair detecting an opposite color, such as red and green, respectively. This pairing means that the cells work together during color detection. After one member of the pair is activated for a few seconds, it gets “tired”, so its partner cell responds instead. For example, when you looked at the image of The Think Tank, your green cells were activated by the body of the Tank, but when you looked at the pink dot after 10 seconds, your pink cells were activated while your green cells were “resting.”

In more scientific terms, color afterimages can be explained by opponent process theory. As described by University of Calgary psychologist Donald Kline, the theory outlines how the cones in the retina are “…linked together to form three opposing color pairs: blue/yellow, red/green, and black/white. Activation of one member of the pair inhibits the other.” In terms of a color afterimage, this means that when the initially activated member of a cone pair (e.g., the red cone) becomes “fatigued”, inhibition of the partner cone (e.g., the green cone) is reduced, making it relatively more active and generating a green afterimage.

Returning one last time to the Tank afterimage activity, the pink and green afterimage you saw demonstrated how just 10 seconds of concentration can literally change how you see color. Now, if 10 seconds can have such an impressive effect on your brain and mind, think about all the benefits to be gained from a longer period of concentration, like when you practice violin every day, or do your homework. That’s neuroplasticity at work – the biological malleability of the brain and mind through experience and practice. As color afterimages show us, this principle is powerful, and seeing different colors is just the beginning.



Chudler, E. H. (2015). The Retina.   Retrieved from https://faculty.washington.edu/chudler/retina.html

Hurvich, L. M., & Jameson, D. (1957). An Opponent-Process Theory of Color Vision. Psychological Review, 64, 384-404.


Kehoe, S. W. (n.d.). Notes for Parents and Teachers on Using Hello, Red Fox with Children.   Retrieved from http://www.eric-carle.com/bb-HRFnotes.html


Kline, D. (n.d.). Theories of Colour Vision.   Retrieved from http://psych.ucalgary.ca/PACE/VA-Lab/colourperceptionweb/theories.htm


Kolb, H. (2016). Simple Anatomy of the Retina.  Retrieved from http://webvision.med.utah.edu/book/part-i-foundations/simple-anatomy-of-the-retina/