According to a link from a Snopes article, yes. http://www.digitaljournal.com/article/326976 http://www.digitaljournal.com/article/326976 In a not so rigorous

According to a link from a Snopes article, yes. http://www.digitaljournal.com/article/326976 http://www.digitaljournal.com/article/326976 In a not so rigorous way, others claim they are. For example: http://nymag.com/scienceofus/2015/02/what-like-see-a-hundred-million-colors.html http://nymag.com/scienceofus/2015/02/what-like-see-a-hundred... Apparently the theory is that a mutation on an X chromosome causes a wonky typically non-functional cone. A male, with one X chromosome gets 2 normal cones and 1 wonky one. A female, with two X chromosome can get 3 normal cones from one X and 2 normal cones and 1 wonky one from the other X, for a total of 4 types of cone. If the wonky one happens to be working they are a tetrachromate. Thus eliminating the gene that causes wonky cones eliminates colour blindness and tetrachromacity. I wonder to what extent the wonky cone in a colour blind male typically functions? They wouldn't necessarily see fewer colours but different colours. The red-green colour blind people I know can still see the colours as different, just not as distinctly based on their saturation, background colour and whether they are doing a direct comparison. Presumably there is also the remote possibility of a colour blind female being a tetrachromate? Additional edit: The world is greyer than something simply functioning or not. Assuming a solid definition of "functioning", something can be partially functioning. More generally, one first has to figure out what functioning means.