Color blindness is not actual blindness, but there is a deficiency of color vision. The most usual cause is a fault in development of one or more sets of retinal cones that perceive color and transmit that information to optic nerve. It's usually sex-linked condition. Genes that produce #photopigments are carried by X chromosome; if some of these genes are missing or damaged, color blindness will be expressed in males more often than in females because males only have one X chromosome.
How Color Blind Are You? This Test Reveals The Truth!