Color is sensed when white light bounces off an object and is reflected into the eye. Objects appear different colors depending on what colors were absorbed and which were reflected. Color is "seen" by the rods and cones in the eye. Cones detect color and rods detect black, white, and shades of gray. People who cannot see colors properly are colorblind. There are many different kinds of colors and they are classified in many different ways (The World Book Encyclopedia p 818, 819).
The eye consists of many parts. The part of the eye you can see when you look at someone consists of four parts. The colored part of the eye where the light enters is called the iris. The white part around the iris is the conjunctiva and episclera. This part also contains blood vessels. The cornea is the clear covering of the iris and pupil. The cornea contains no blood vessels. The lens is located behind the iris. The lens is used to focus, as in the cornea, but the lens can move. The retina is responsible for telling the brain what a person is seeing. They determine all the different parts of what is being seen. It then codes them to electrical signals for the brain (Cassel p 4-10).
Rods and cones are in the retina. There are three kinds of cones. Each cone can sense a different color. Rods are used when a person is in dim light (Hubel p 162). The optic nerve is what sends all these messages to the brain (Cassel p 261).
Sometimes people have difficulty telling colors apart. This is called colorblindness (Webster's Dictionary, p 281). Sometimes colorblindness is hereditary. Other times there is a problem with the message reception from the optic nerve. Another problem can lie in the retina. People can have trouble recognizing colors because of certain drugs.
People are diagnosed as being colorblind by taking tests. They look at different colored numbers that are in order by their color. This way they can be diagnosed as being colorblind in certain areas (Cassel p 52). A person can have different extents of colorblindness depending on what the problem is. A person can be colorblind because they have too few of a certain kind of cones or because they have too many. The more problems a person has, the more colorblind they will be (Hubel p. 172).
Color perception varies from place to place. Some cultures have only a few colors that are distinguished from one another. Some cultures do not separate green from blue and yellow from orange. Other cultures have more specific names for things that are important to them. Eskimos have seventeen words for white because of all the snow.