Most color perception defects are for red or green or both. Red-green color deficiency is a result of a lack of red receptors. It is also possible to have the color receptors missing entirely, which would result in black and white vision. The earliest years of education use color as a teaching method and colors such as red, yellow and green are heavily employed. Many who have color vision defects are unaware of their problem especially grade school children.
Teachers then think they are slow or have learning difficulties.
Affected children have to learn how to distinguish colors in terms of luminance contrast differences. Particular attention must be paid to pupils who seem to be color deficient. Children who are 5 or 6 years old should be able to use color names correctly. Six year olds and older children should match colors of varying hue and saturation. In order to avoid misunderstandings, teachers should adapt their teaching methods to color deficient pupils.