An example of the location would be a stoplight. The person would be taught that the red light is at the top, the yellow in the center and the green at the bottom. Another would be to learn that a stop sign is red, a yeild sign, and so forth. Sometimes, specially tinted eyeglasses can help. Check with your ophthalmologist if you suspect you are color vision deficient, to see which of these devices would be right for you.
Color blindness is essentially a defect.
It is caused by a defect in the retina or the nerves of the eye. The first documentation of this disorder was made by a British Chemist named John Dalton, who did, in fact, suffer from this disorder. Total color blindness in which all color is seen as shades of gray, only, is called achromatopsia or monochromatism, is extremely rare. More common is partial color blindness. This type is technically termed dichromatism.