Colour blindness refers to when an individual is unable to distinguish one certain colour from another. As it is sex-linked colour blindness is more common in males then in females. The most common colour blindness is red-green colour blindness and is a result of either the red sensitive or green sensitive cones are absent causing the individual to either see all colours other than red and green or have trouble distinguishing between red and green. A rarer type of colour blindness is blue-yellow colour blindness where the blue sensitive cones are absent and the individual may have trouble distinguishing between blue and yellow. Total colour blindness, where all Red sensitive, green sensitive and blue sensitive cones are absent, causes the individual to only see black and white images however this case of colour blindness is extremely rare.
From the information presented above it is evident to see how colour blindness in humans is the result of one or more of the colour sensitive pigments missing from the retina.



http://www.youtube.com/watch?v=1-KzJ7_BuXM is the video above which gives a good explanation of cones within the eye and the absence of colour sensitive cone resulting in colour blindness.



Aubusson, Eileen Kennedy Peter. Biology in Context: the Spectrum of Life. Victoria : Oxford Uni. Press., 2001. Print.
"HSC Online." NSW HSC Online. N.p., n.d. Web. 25 June 2010. <http://www.hsc.csu.edu.au/biology/options/communication/2952/CommPart4.html#1>.
"YouTube - How the Body Works : Color Vision ." YouTube- Broadcast Yourself.. N.p., n.d. Web. 27 June 2010. <http://www.youtube.com/watch?v=1-KzJ7_BuXM>.