Poor color vision is a reduced ability to distinguish between certain colors. Although many people use the term "colorblind" to refer to the reduced ability to discriminate between colors, true colorblindness is a total lack of color vision, which is rare.
Poor color vision is usually inherited. Men are more likely to be born with poor color vision. Most people with poor color vision can't distinguish between certain shades of red and green. Less commonly, people with poor color vision can't distinguish between shades of blue and yellow.
Certain eye diseases and some medications also can cause poor color vision.