People with normal color vision can perceive numbers formed by patterns of colored dots in every circle. If you do not see some of the numbers, you should have your eyes checked and consider working in a job where color discrimination is not critical.
Approximately 6%-8% of people of European descent, 4%-6% of people of Asian descent, and 2%-4% of people of African descent have some type of defective color vision. Images based on Tests for Colour Blindness by Dr. Shinobu Ishihara.
 25 |  29 |
 45 |  56 |
 6 |  8 |
As an experiment, look at these circles with blue-red 3D glasses, first with one eye, and then with the other. Some of the numbers will not be visible! Also, use the glasses to look at the word color test below and explain the results.
BLACK RED GREEN
PURPLE YELLOW RED
ORANGE GREEN BLACK
BLUE RED PURPLE
GREEN BLUE ORANGE
This is a type of psycholinguistic test that poses some difficulty because the portion of the brain that handles language has the conflicting tasks of verbalizing the color of the written words while ignoring the meaning of words representing colors.