People who are colorblind usually have difficulty with the colors green, yellow, orange and red. Color blindness is inherited and is caused by a lack of specific color-sensitive cells in the eye. More boys than girls are affected by color blindness.
Colour blindness - Better Health Channel. (2014, March 4). Retrieved November 5, 2014, from http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/colour_blindness