What is the rarest color in nature? - Victoria Hwang
Every color you see in front
of you can be found in nature.
Some plant, animal, or mineral
bears almost every hue imaginable.
But which of these colors are you
least likely to see in the natural world?
There are two factors that drive
the rarity of color in nature:
physics and evolution.
Let’s start with physics.
Colors are generated when wavelengths
of light interact with objects,
and most of the colors
you’ve seen outside a screen
were produced in one of two ways.
In absorption-based colors,
certain wavelengths are absorbed
by an object, while others are not.
The result is a matte final color
generated by these leftover light waves.
Most naturally occurring colors
fall into this category,
including those of many fruits
and flowers.
Plants are full of compounds called
pigments that absorb light waves
as part of photosynthesis,
the process by which
they convert sunlight into energy.
While different plants have evolved
different pigments
that result in different colors,
higher energy wavelengths are more easily
absorbed than lower energy ones.
And blue light has some
of the highest energy wavelengths
in the visible spectrum.
Numerous pigments have evolved
to absorb blue light,
including chlorophyll, which absorbs blue
and red wavelengths
to produce nature’s trademark green.
However, green light is still
fairly energetic,
and the most common class of pigments
evolved to absorb these wavelengths
as well.
There are over 1,100 types
of carotenoids,
pigments which absorb high energy
blue and green light,
while leaving behind the lower energy
red and yellow light.
While carotenoids are present
in most green plants,
they only become visible each fall
when chlorophyll gets broken down
to save energy for the winter.
But whether they’re working alone
or side by side,
these pigments absorb
blue light in virtually all plants.
Even fruits and flowers that appear blue
actually have pigments
that are red or purple,
and only truly turn blue
under specific chemical conditions.
So, is blue the rarest color
in nature?
Not quite.
Absorption is just one of the two
main ways light generates color.
In the second method, some wavelengths
are scattered and amplified—
overpowering the others to determine
an object's final color.
These structural colors occur
because some objects around us are made
of microscopic particles
which can form nanostructures
that interfere with visible light.
For example, this feather has
no blue pigments in it.
But when light strikes it,
the electrons within its nanostructure
vibrate at the same frequency
as the wave.
This makes the particles send
out a new wave with the same frequency,
starting a chain reaction that amplifies
and scatters blue light.
Nanostructures of various shapes and sizes
scatter different wavelengths,
but they typically scatter high-energy
wavelengths most easily—
making blue
the most common structural color.
Meanwhile, low-energy wavelengths
like red are only weakly scattered.
Even when something evolves
specific nanostructures
that strongly scatter red light
they still resonate
with other wavelengths,
only appearing red at some angles
of illumination and observation.
This gives us two contenders
for nature’s rarest color:
absorption-based matte blues
and structural iridescent reds.
Between these two,
structural reds are much rarer.
Only a handful of animals and rocks
scatter red light
and none of them scatter
red light exclusively.
But since red and blue are rare
in one way and common in another,
we actually end up seeing
both colors quite often.
So what color is least likely
to be generated
in structural and absorption-based forms?
The answer is violet.
Not to be confused with purple, which is
just a combination of red and blue light,
violet occupies a small portion
of the visible light spectrum.
There are only a few nanostructures
precise enough
to exclusively scatter violet light.
And violet wavelengths are even
more energetic than blue ones,
making them likely to be absorbed
by pigment.
So if you ever stumble
onto the iridescent violet wings
of a purple emperor butterfly,
take a second to appreciate
one of nature’s rarest spectacles.
