All the colours of the spectrum come from three primary colours: Red, Green and Blue.
- 4% of all males and 0.5% of females are colour deficient. This means that one of the primary colours is missing from their perception.
- The colour spectrum is skewered and fewer colours are perceived.
- This can obviously have devastating effects for people who operate in colour coded environments such as an Industrial Plant.
Traffic lights, for example, are manageable mostly because there is a difference in the brightness or luminosity as well as a general recognition of the position of the lights.
Cooking and foods:
When cooking, red deficient individuals cannot tell whether their piece of meat is raw or well done. Many cannot tell the difference between green and ripe tomatoes or between ketchup and chocolate syrup.
Some food can even look definitely disgusting to colour deficient individuals. For example, people with a green deficiency cannot possibly eat spinach which to them just looks like cow pat. They can however distinguish some citrus fruits. Oranges seem to be of a brighter yellow than that of lemons.
Ishihara Colour Deficient Test
This is the one most common test used. Although there is no treatment for deficiency, most deficient persons compensate well and may even discover instances in which they can discern details and images that would escape normal-sighted persons. At one time the U.S. Army found that colour-deficient persons could spot “camouflage” colours where those with normal colour vision are fooled by it.