Color changing fish!

  1. A black marker or a black sign pen
  2. Red, green & blue (RGB!) construction paper
  3. 4 sheets of white pape
  4. Scissor
  5. Glue 
    [All the materials can be obtained from a general store or a convenience store]
    Red Paper Fish

  1. At first put the red, green and blue construction one over another.
  2. Now draw the outline of a fish on the topmost construction paper.
  3. After that, use the scissor to cut the outline of the fish from all the construction at once. So now we have 3 paper fish with red, green and blue colors.
  4. Use the black marker or sign pen to draw the eye of the fish on each cutting. Now we have 3 paper fish.
  5. Glue each paper fish onto different pieces of white sheet. 3 out of 4 white sheets are used. So now we have only 1 white sheet.
  6. On the last white sheet let’s draw a large fishbowl. Large enough to fit one of our paper fish inside the drawing.
  7. Lay one paper fish and the fishbowl drawing next to each other on a plain surface.
  8. Now stare at the paper fish’s eyes for about 20 to 30 seconds. Then quickly stare at the fishbowl drawing.
  9. Record what you see.
  10. Now repeat the same process for the other two paper fishes and record your observation. 


  1. After staring at the red paper fish you should see the shape of a blue-green colored fish in the drawing of the fishbowl.
  2. After staring at the green paper fish you should see the shape of a magenta colored fish in the drawing of the fishbowl.
  3. After staring at the blue paper fish you should see the shape of a yellow colored fish in the drawing of the fishbowl.


In the article “Black & white - Source of colors!(BENHAM’s disk)” we were able to learn that in the retina of our eye there are some special cells called cones which are responsible for vision. In this experiment, the imaginary image which we see on the white paper after staring at any colored paper is called an afterimage. It’s called afterimage because it appears after the real stimulus is removed. This case of afterimage results when our cones gets tired.

For example, when we look at the red paper fish, the image falls on one part of the retina. The red sensitive cones in that area gets tired over time and stop responding to anything. So after that when we turn to look at the white paper, the red sensitive cones are too tired to respond to anything by then. Our eyes only see white when all three types of cones respond equally. So, when the red sensitive cones gets tired, it creates an imbalance and a color other than white is seen. The only cones responding at that time are the green and blue cones. That means the fish afterimage we will see should be blue-green color. Similar events occur with the other colored paper fishes.

Use other colored paper fishes to see the effects and record them.


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