I think that so far I familiarized you with the eye test illusion and also with the colorblindness tests. To summarize from the beginning: if you are colorblind you will be able to distinguish only two colors in the next picture. In this illusion although there is another element we haven’t talked about so far.
What to see?
The picture represents a spiral made out of many colors that interfere one with another creating also a dizzy motion or a tiring. Try to count the colors in this spiral! Most of us will probably see four colors and in a way it’s right. If you want to discover the real number of colors try to enlarge the image and you will see that they are actually three colors: pink, orange and green.
How it works?
The fourth color appears because some colors in association with others create the impression of a totally new one. In reality the picture has only three colors: green, pink and a shade of orange. The blue appears because the influence of the pink and orange. Because green and pink/red are complementary colors when they are intersecting the shade of green changes into blue, but when the green is combined with orange it remains the same.