The Ishihara Test for Color Blindness
The Ishihara test is commonly used to detect Daltonism (color blindness of basic colors: red, blue and green).
A distinction is made between:
protanopes, who do not see red; deuteranopes, who do not see green; tritanopes, who do not see either blue or yellow.
Tritanopes cannot be identified using an Ishihara test but instead requires a 100 Hue test, which needs to be carried out by your eye care specialist.
Rarer are people with complete color blindness, who only perceive levels of gray. They are said to suffer from achromatopsia.