Color vision deficiencies may be partial (affecting only some colors) or complete (affecting all colors). Complete color deficiency, also known as color blindness, is rare. More often, individuals have a deficiency with one of the three photosensitive pigments in the eye: red, green or blue. Those people with normal color vision are referred to as trichromats. People with a deficiency in one of the pigments are called anomalous trichromats (the most common type of color vision deficiency). A dichromat has a complete absence of one cone pigment.
The most common signs of color vision deficiency are difficulty distinguishing between reds and greens or difficulty distinguishing between blues and greens. There is no cure for color vision deficiency. However, those with mild color vision deficiencies can be taught to associate colors with certain objects. In some cases, color vision deficiency can affect child development and career choice, which is why early detection is critical.