Colour perception is usually testes using the Isihara Test charts. These charts are designed to test for the typical red-green deficiency. People with red-green colour perception deficiency perceive some colours as gray and therefore label them differently than people with normal co lour perception.
The Isihara Test is a circle of multicoloured dots in which there is imbedded a number. In some cases people with normal colour perception see one number while people with colour perception deficiency see another number. If 10 or more of the plates are read correctly the colour perception is considered to be normal. If 7 or less of the plates are read correctly then the colour vision is considered to be deficient.
This Isihara plate is designed to identify people with Protanopia (long wave red deficiency) and Deuteranopia (middel wave green deficiency). People with mild red-green deficiency will see 96, but people with Protanopia will see only 6. People with Deuteranopia will see 9 only.
The Vision Training approach attempts to encourage finer hue distinctions which in turn develop better colour perception. Training is only effective for the common red-green colour perception deficiency.