Ishihara Test for Color Blindness
Courtesy of the Howick Volunteer Coastguard

What numbers do you see revealed in the patterns of dots below?

Normal Color Vision

Red-Green Color Blind

  Left Right   Left Right
Top 25 29 Top 25 Spots
Middle 45 56 Middle Spots 56
Bottom 6 8 Bottom Spots Spots

Another interesting color blindness test is below

The test to the left is simpler.
The individual with normal color vision will see a 5 revealed in the dot pattern.
An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.