People who cannot tell all colors apart are said to be color-blind. Most color-blind people can see yellows and blues, but confuse reds with green. It is very rare for a person to be blind to all colors, but they may see everything in shades of black, white and gray. It is interesting to point out that many color-blind people don't even realize that they are color-blind, they don't know that the colors they are seeing and naming are not the actual colors that people with normal vision can see. This can be dangerous when a color-blind person confuses the red and green of a traffic light. Color blindness is thought to be inherited and although doctors have tested color blindness, there is no cure to treatment for it. A color-blind person  _  .
always knows how color-blind he is often gives the wrong name of colors see everything as the same color can hardly see something of strong colors