Color blindness or color vision deficiency is the inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired. "Color blind" is a term of art; there is no actual blindness but there is a fault in the development of either or both sets of retinal cones that perceive color in light and transmit that information to the optic nerve.
The symptoms of color blindness also can be produced by physical or chemical damage to the eye, optic nerve, or the brain generally. These are not true color blindness; however, but they represent conditions of limited actual blindness. Similarly, a person with achromatopsia, although unable to see colors, is not "color blind" per se but they suffer from a completely different disorder, of which an atypical color deficiency is only one manifestation.
Here is a Test which is called Ishihara Color Blind TestNormal Color Vision will see Red-Green Color Blind will see
Left Right Left Right
25 29 25 Only Spots
45 56 Only Spots 56
6 8 Only Spots Only Spots