Colour vision and colour blindness

Color vision is the capacity of an organism to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. Certain colors give us information while driving such as red and green. Certain colors can calm us like light blue, some colors can improve our concentration like yellow. The perception of color can be varied. Approximately 10% of the people perceive color inaccurately.

The sensation of color is caused by brain. The main way to get it is the response of the visual system to the presence or absence of light at various wavelengths.
Isaac Newton gave the idea that white light is light containing all wavelengths of the visible spectrum.
He demonstrated this fact with experiments on the dispersion of light in glass prisms.
Thomas Young in 1802 speculated that there were three different types of color sensitive receptors in the eye.
Causes of color:
A red apple does not emit red color. Rather it absorbs all the wavelengths of the light except the frequencies responsible for red, which is reflected. Light enters the eye and stimulates cone photoreceptor in the retina according to varying wavelengths. Then the information travels via optic nerve to visual cortex where processing takes place and we perceive it. Physiology of color perception: Cells which help us to perceive light can generally be divided into cones and rods. Cone cells help us to see color and during daylight. Rod cells are generally more responsible for nighttime vision. There are generally three types of cone cells responsible for color vision. They include "red," "green," and "blue." cells. Normally we have all three types. This confers trichromatic color vision, so primates, like humans, are known as trichromats. Many other primates and other mammals are dichromats, and many mammals have little or no color vision.

Colour Vision | Introduction to colour blindness | More on colour blindness