Re: how do non-living things get their colors?

Dear Jeff, 

Color is actually a very complicated thing.  Non-living things get their 
colors in the same way that living things get their colors.  First, lets 
talk a little bit about the nature of light.

You may  already know that light is made up of many different colors (some 
would say "all the colors", but that is not quite exact).  Light is actually 
made up of "electromagnetic" signals, just like the signals that carry your 
favorite radio and television shows or the signals used to take an Xray of 
your broken toe.  These signals travel in "waves".  The signals can be 
categorized by the length of one wave - which is oddly enough called the 
"wavelength".  The light from the Sun, stars, and many other sources 
contains light waves of many different wavelengths.  Some of these you can 
see and some you cannot.  Actually, the wavelengths that we can see makes up 
a very small part of all of the wavelengths that are in light.  (All of the 
wavelengths together are known as the "electromagnetic spectrum".)

Now here's the tricky part.  Our eyes have several different kinds of cells 
in them.  Some cells, called cones, detect specific wavelengths, or colors, 
of light.  There are three types of cones.  One cone detects the wavelengths 
of light we call "green", another detects the wavelengths of light we call 
"blue" and a third detects the wavelengths of light we call "red".  When 
light reaches our eyes, it may have wavelengths in each of the colors, but 
in different proportions (in other words, there might be more green than red 
or blue).  Each type of cell will get "excited" if the color it is designed 
for is included in the light.  The amount of "excitement" will depend up on 
the amount of light of that color.  The excited cell sends a signal to your 
brain that tells the brain how excited it is.  Your brain then interprets 
the color of the light based on how much each type of cone cell is excited.  

For example, if you look at a green piece of paper, the green cones in your 
eyes get very excited, but the red and blue cones don't.  Your brain 
interprets the signal it receives as the color "green".  Now, if instead you 
had a yellow piece of paper, then the light will excite both the green AND 
red cones in your eye, but not the blue cone very much.  Your brain 
interprets the excited signals from the green and red cones as the color 
"yellow".  If the light excites all of the cones equally, the color gets 
interpreted as "white" by your brain.  If none of the cones get excited, 
then your brain interprets the color as "black".  SO, all of the colors that 
you see are made up by your brain based only on the red, green and blue cone 
cells!  

Here's a simple experiment:  If you look very closely at a television or 
computer monitor with a magnifying glass, you will see tiny red, green and 
blue dots.  These dots create the colors you see on TV or your computer by 
sending light to your red, green and blue cones.  Isn't that amazing?? 

(Did you know that many animals, like cats and dogs, don't have cones.  They 
don't see colors.  To them the world looks like an old "black and white" TV 
show.) 

So why do things have colors?  Well it all goes back to the light.  When an 
object is in the dark, do you see any color?  No, of course not.  That's 
because when there IS a source of light, it reflects off of an object so you 
can see it.  If there is no source of light, there is no light to reflect 
and you cannot see it.  

Some materials reflect almost all of the light - like a blank piece of paper 
for example.  The reflected light, in this case, excites all of the cones 
equally.  But if you look at the leaves on a plant, they look green because 
the material in the leaf (cholorphyll) reflects only the green light.  What 
happens to the other colors of light?  Well they get "absorbed" by the leaf.  
That absorbed light gives them ENERGY so they can grow and live.  

So what about the color of non-living things?  The same thing happens.  If 
light reflects off of a green object (green piece of paper, or a green 
stone, or green paint) the object absorbs the light that is not green and 
reflects the green light.  If something appears black, then it absorbs ALL 
of the light.  

But non-living things don't need ENERGY to grow - what happens to all of 
that absorbed light?  It turns into heat.  Have you ever stepped on a black 
driveway and then a white sidewalk in your bare feet in the summer?  If you 
have, then you know that the driveway is MUCH hotter than the sidewalk.  
This is because the driveway absorbs almost all of the light that reaches 
it, but the sidewalk does not.  

I hope that this answers your question, Jeff.  I know that it was a rather 
long answer, but as I said at first, color is a complicated thing.  So next 
time you pull out the crayons and paints, think about how your eyes and 
brain work together to see colors and the beautiful pictures you create with 
them.

Best regards, 
Todd Jamison
Chief Scientist, Observera, Inc.

PS If you have any related questions, you can email me directly at 
tjamison@observera.com