To a person familiar with the workings of human color vision, this statement says the speaker has no red-sensitive cones on his retinas:  He is protanopic.

Ordinary human color vision has three dimensions of color corresponding to the blue-sensitive cones, the green-sensitive cones and the red-sensitive cones.  Protanopic vision has only the green-sensitive and the blue sensitive dimensions.

2-D.............	3-D
PROTANOPIC	NORMAL COLOR

Our knowledge of color is determined by Mother Nature's evolutionary design of our eyes, a process which took very different routes for different creatures.  Those differences tell us just how limited our perception really is.   Many creatures have known for millions of years things we have discovered in just the past few centuries.  We are not "the measure of all things."  It's a bit self-centered and conceited to think we might be.

Rich as is the color we see with our three dimensions of color vision, birds have vastly richer color vision, color which extends beyond our paltry three dimensions.  Birds have four cones and probably have other visual mechanisms that take the dimensionality of their color to five or six.  (Colored droplets of oil on their retinas.)

We cannot experience the color seen by a bird; we can only devise mathematical tools that let us ask and answer questions about it.  The concept of dimension of color is subtle enough that producers of a PBS series demonstrated that they had misunderstood it (SEE).

Those who master such math have a lopsided advantage over those who know nothing of such powerful techniques.  On the way to such mastery we will master some understanding of many-dimensional spaces--a good place to start is to look at some of the interesting things about those color arrays of color vision.  (And how would you rank people by their size?.)  This is the mathematical world of vectors and tensors.

Richard Feynman, whose insight into the subtle aspects of the world seemed magical to those who knew him, once said, "Since most of you are not going to become physicists, but are going into the real world...sooner or later you will have to use tensors." (SEE)  What a strange statement! 

As we better understand his meaning, we better understand a lot of really severe oversimplifications we probably never realized we were making.  Dimensionality in measurement (vector, tensor, complex number, quaternion, etc.) challenges virtually everyone's thinking skills and insights, but it's a challenge well worth meeting.

Follow these mysteries and discover how our most common ideas of human intelligence and of distributing wealth are reqlly bizarre.
 

Colors seen if no green cone (deurternopia).  Still two dimensions to depict because there are still two  kinds of cones.  MORE
 
 
 
 
 
 
 

Other creatures have perceptions we lack and know things we must use science and math to discover.
 

That bird with the great color vision knows someting about sunburn and sun tan that few human know -- but should!