Human eyes have an average of 4.5 million color-sensitive ‘cone’ cells in that middle part of the back of the eyeball called the fovea (Latin for ‘small pit’). 

Stop now.  Try to stare straight at these words and, without glancing sideways, describe the color of something off to the side (a folder or a book cover or some other object).  You can’t do it, can you?   When you turn your eyes to the side, the folder is obviously yellow, the book cover is clearly green, and that flashlight is quite orange.

Did the objects become yellow, green, and orange because you looked at them, or were they yellow, green, and orange before you looked at them?  We’ll leave that to philosophers.

We know that human eyes with their cones are of three types, and here’s what frequencies of electromagnetic emissions they’re sensitive to.  For those who want to know the three parts of the visible color spectrum the cones in humans respond to, this should help.  (Yes, there is an overlap!)

Humans are blind to ultraviolet light – or infrared light – but not all animals are.  Bees and butterflies see ultraviolet areas of flowers that you and I and every living human have never seen and never will see.  (I’d show you a picture of what they could see, but that would be pointless, wouldn’t it?  You wouldn’t see the ultraviolet areas because  you are neither a bee nor a butterfly!)

Don’t feel bad, though.  At least you can see colors far better than dogs can!  They only have cones sensitive to blue and yellow.  See?

.

So what colors do most humans see?  (Remember, some are color blind, so we say “most”!)  Here’s one schematic that might help and might not.  If you’re curious, Google “1976 CIE Chromaticity Diagram” and prepare to be confused.  It’s ok to be baffled, by the way.

So, now we know it all?  Uh, sorry.  Mantis shrimp have 12 different cones in their light-sensitive organ that we’ll call “eyes,” – but humans perceive colors better than they do.  (Experiments!)

So, where does that leave us?  Well, that’s another topic we won’t discuss today: the human brain, specifically the occipital lobe (from the Latin word for ‘back of the head’).  That’s where all the incoming signals from those cones are turned into something called “color.”  

Once again, time to turn this over to the philosophers to talk about the word ‘perceive.’   Bye!