His mother is heterozygous for color blindness. This type of condition means that some people will have trouble distinguishing one color from another color. This color vision deficiency is more common among males rather than females but it does not mean that you will not meet women who are colorblind.
Take note that there are three different types of color blindness. The red-green color blindness is the type of color blindness that people usually suffer from. The blue-yellow color blindness is known as a close second while color-vision blindness means that people may see things without any color at all.
