Comparing Yellows

Does everybody see the same colors that I see?

disagreeing about color
Digital camera view of Comparing Yellows,
As viewed by the exhibit creator, the dot at 5 o'clock is the closest in color to the center dot.

With 10 or more people look at the exhibit Comparing Yellows.




red and green filters

To Do and Notice

What do you see?

Many groups report that they see a central dot of color which looks yellowish-tan surrounded by an arc of colored dots ranging from greenish at 7 o'clock to reddish at the 5 o'clock position.

I ask them which of the outer arc of colored dots most closely matches the central dot.

I point at the dots one at a time while people raise their hands. Some people see that different outer dots match the central dot in color. It is important to be honest.

What's Going On?

The central dot is composed of light with one wavelength*, it is seen as yellow.

The outer ring of dots is each made of a mixture of two different wavelengths of light, one which by itself is seen as greenish and another which is seen as reddish. However the amount of green and the amount of red is different for each different dot.

DisagreeingAboutColorRed Disagreeing about color green
The left image has a red filter held over the central dot and the dot at 5 O'Clock, The right image has the red filter over the central dot nad the dot at 7 OClock.

Notice there is no red light in the central dot, and that there is mor red in the 5 O'Clock dor than in the 7 O'Clock dot.

Most people see the dots near 2 o'clock as the ones that most closely match the central dot.

Some people give wildly different answers. (The exhibit builder designed the exhibit so that the dot at 12 o'clock most closely matched the central dot in his perception.).

People have different numbers of cone cells which detect colored light. Some with no cones which respond to one region of the spectrum are said to be colorblind. From one person to another there can be small differences in the numbers of each type of cone and also differences in the chemicals which detect the light, these variations lead to different perceptions among viewers. The variation in perception from the average is known as anomalous color perception. Some people, 1 in a million, have no cone cells at all, some have 4 cone cells, they have an extra green cone that lets them detect subtle differences between green and blue.

A question answered

Thus you can see that two people can look at the same light and see different colors.
It's hard to believe that there can be such a simple answer to such a difficult sounding question.

So What?

Some people are colorblind, they give wildly different answers to the question of which dots most closely match. Yet others who can pass the standard colorblindness tests also disagree about which dots match in color.

There seems to be a spectrum of colorblindness.

Going Further

Try observing this exhibit from a greater distance. Notice how your perception of which color matches depends on distance.

Take photos of the exhibit with a camera, notice which colors the camera protrays as identical.

Look at the dots through a red filter and a green filter. Notice how the combination of red and green light in the outer arc changes from more green at the 7 o'clock position to more red at 5 o'clock.

When you are done with this exhibit step over to the exhibit "Seeing Yellow" and conduct some more experiments. At seeing yellow you can adjust the red and green lights until they match the yellow light. Then ask a friend to do the same. You can also create your own experiments.

Seeing Yellow exhibit
The Seeing Yellow Exhibit.
The left bar of color is a mix of red and green, the right is pure yellow.
The two bars are adjusted to be identical to my eye, they are not identical to the camera.


Oliver Sacks has a book about an island in the pacific where many people have no cones and so see only in black and white. The title of the book is "The Island of the Colorblind." Oliver Sacks was an Osher Fellow at the Exploratorium.

*It's more complicated than that. The yellow light of the central dot has a small range of wavelengths not exactly one wavelength. Return.

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Scientific Explorations with Paul Doherty

© 2002

18 September 2002