The human eye sees by light that reflected to it and stimulating the retina. The retina is a a neuro-membrane lining the inside back of the eye that made up of what are called Rods and Cones. When the eye received light the Rods can translate the light to shape an image of what you see in your brain but can not distinguish the colors. Cones in the other hand is the one responsible for processing the colors to your brain during the daylight.
Each visible color has a different wavelength that can be absorbed by a light sensitive pigment that is located in the cones. Genes are the one that contain the coding instructions for these pigments. These pigment can read the colors by their wave and translate it. So if there is something wrong in the instructor of the coding, the pigments will read a different color wave, and that what cause the color deficiency.
Color vision deficiency can be the inability to distinguish certain shades of color or in more severe cases, see colors at all. The color blindness is divided to three types:
A. Red-Green color blindness.
which is the most common type due to loss or limit function os the red photopigments.
B. Blue-yellow color blindness.
this type is less common than the red-green color blindness and it caused due the missing or loss the function of the blue photopigments.
C. Complete color blindness.
Complete color blindness is the disability to see colors at all, and it's really rare type of Color vision deficiency .
the color blindness can be diagnosis by different tests but the most common test is the Ishihara Color Test. The Ishihara test is a given circle that contains dotes that have different sizes and colors.
these dotes together are shaping a number or picture that is difficult for people withe Color vision deficiency to see.
References:
http://colorvisiontesting.com/color2.htm
http://www.mushaboomdesign.com/Pages/technical/05_06_digitalprinting.html
https://nei.nih.gov/health/color_blindness/facts_about
http://sangkrit.net/how-to-daltonize-your-web-browsing-experience-on-google-chrome/
