Color blindness is a common problem that occurs when some of the cones in the eye are missing. (Remember that cones sense color and rods sense light/dark.) |
There are actually three kinds of cones: cones that sense the color red, cones that sense green, and cones that sense blue. Red, green, and blue (light, not paint) are three colors that can be mixed to make white (light). When some of these cones are missing, certain colors look that same, like, in your father's case, red and green.