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Originally Posted by Faetyl
FYI - The only trickery here is in your brain. 
[left]If your eyes follow the movement of the rotating pink dot, you will only see one color, pink. If you stare at the black + in the center, the moving dot turns to green. Now, concentrate on the black + in the center of the picture. After a short period of time, all the pink dots will slowly disappear, and you will only see a green dot rotating if you're lucky! It's amazing how our brain works. There really is no green dot, and the pink ones really don't disappear. |
The disappearance is due to desensitization. Where the optic nerve gets desensitized to the color (pink in this case) and therefore stops "sending" pink signals to the optic processing area of our brain. In dentistry and in dental lab it is called Metamerism: the phenomenon exhibited by pairs of color metamers <the problem of metamerism in matching artificial with natural teeth>.
This happens a lot in the dental field. If you notice, most patient napkins (the thing around your neck) is blue. Some clinics use different colors, but predominantly they are blue. It can depend on the type of dental work being done as per the color choosen by the practitioner. If the dental work being performed is crown and bridge work, the napkin is usually blue. Why, you ask?
The color blue is a very neutral color to our optic senses. By using blue, the dentist or their assistant can glance at the napkin, to relax their eyes. This allows them to give their optic nerve a rest from "white or tooth" colored objects. By seeing blue, the eye relaxes, and the nerve once again becomes sensitive to the tooth's color. This allows the person looking at the tooth to correctly match the shade of the tooth to the shade of the crown that is going to be made.
As in the graphic demo above, the pink is slowly taken out of your vision due to the desensitizing affect. Glance away for a moment, even a split second, and your will once again be able to see the pink color again.