I came across a very interesting article today stating that the number of cones in the human retina can vary by a factor of 40 from person to person. This just goes to show that there are nontrivial social and cognitive variables at work here. 
 
An interesting quote: 

Over time, we were able to shift their natural perception of yellow in one direction, and then the other," says Williams. "This is direct evidence for an internal, automatic calibrator of color perception. These experiments show that color is defined by our experience in the world, and since we all share the same world, we arrive at the same definition of colors.

Posted by: Matt Morris