Just because we see something in a certain way doesn ’ t mean that everyone else will see it in the same way . In fact , even under imperceptibly different conditions , we may not see it in the same way either !
COLOUR BLINDNESS is the inability to distinguish certain colours . It occurs when one or more of the retina ’ s three photoreceptor cone cell types are either absent , deficient , or there is a fault in the signal pathway between the cones and the brain . Most cases are hereditary .
Trichromatism is colour vision based on the perception of the three primary colours of light : red , green , and blue . Humans are generally trichromats , meaning that normal vision consists of three distinct and functioning retinal cone pigments .
Dichromatism is colour vision based on the perception of two primary colours of light - ie , it is the complete deficiency of one type of cone pigment . There are three types of dichromatism depending on which one of the three normal pigments is missing : » Protanopes are the most common and lack red sensitive receptors . » Deuteranopes lack green receptors .
Protanopes and deuteranopes cannot distinguish red from green light . This is the most common hereditary colour vision defect ocurring in 8 % of males and 0.5 % of females .
» Tritanopes lack blue sensitive receptors and cannot distinguish blue from yellow .
Monochromacy or Achromatopsia is complete colour blindness , wherein only black , white , and shades of grey are perceptible . It is extremely rare occurring with an incidence of about 1 in 30,000 .