More than 14 million people in the U.S. and Canada are afflicted with some type of color vision deficiency ranging from mild to severe which makes it impossible for them to see colors that normal-sighted people see– and to tell different colors apart from one another.
With almost 60 million people seriously involved in photography, (excluding snapshooters) more than 2.5 million of them have color vision problems; you may be one of them or know someone who is.
Read this article on how help is underway for those that are color blind.