[music playing]
Sometimes nature
plays tricks on us.
What we think we know
to be true may not be.
Animals, for example,
have lots of secrets,
like their remarkable
use of color
to attract mates or disguise
themselves from predators.
Well, it turns out
they've been using
colors in ways that have been
tricking us humans as well.
We reached out to the Explorer
and [inaudible] communities
to crowdsource this special
Explorer segment, True Blue.
[music playing]
NARRATOR: White, black,
red, green, yellow.
Animals have evolved to
come into every color
of the rainbow.
But with few exceptions.
Animals are not blue.
For animals most color
comes from pigments,
color chemicals that are
produced by special cells.
Pink, orange,
chartreuse, animals
can produce many different
types of color pigment,
but blue is a problem.
NARRATOR: Some
animals appear blue,
but they're deceiving you.
SARAH GARRET: Instead
of using pigments,
most blue animals have developed
a way to trick your eyes
and play with light,
using physical structures
to appear blue.
Most of the blues you think
you know really aren't blue.
[music playing]
NARRATOR: Humans can only
see light in what we call
the visible spectrum,
a narrow band
of electromagnetic wavelengths.
Color is how we perceive
different wavelengths
of light in that spectrum.
And that visible spectrum
contains all the colors
that we see in this world.
SARAH GARRET: This is the
blue morpho butterfly.
Yes, the emoji one.
It is the perfect example of
an animal that only appears
blue because of the
clever way that its wing
scales interact with light.
Similar to how a prism disperses
different wavelengths of light,
a blue morpho wing has
microscopic structures
that scatter light to
cancel out other colors,
reflecting only blue.
This is based on how
the light reflects.
As you change your
viewing angle,
different colors
appear stronger,
giving us an
incredible iridescent
effect, the tell tale
sign of a fake blue.
And because that reflection
is based on the structure
of the wing, if you filled
that structure with something
different, say, alcohol,
that color would change.
Don't worry.
It dries back to blue.
Many other animals use
physics to deceive us.
For example, there are no
blue feathers on birds.
All birds that appear
blue have some structure
in their feathers that
reflects only blue light.
And almost all fish
use light scattering
to create their vibrant blues.
Less than 1% of the animals
that you perceive as blue
actually have any
blue pigment in them.
That 1% with blue are very rare.
They are true blues.
[music playing]
NARRATOR: This is the
olivewing butterfly.
It's one of very few insect
species on Earth known
to have a true blue pigment.
This is the blue
poison dart frog,
one of the only vertebrates
known to contain blue pigment.
No matter how you look
at them, they're blue.
All of the other animals
only appear blue.
You may perceive blue, but it's
because these animals have all
evolved a way to
trick your eyes,
using the physics of light
to control what you see.
But why blue?
Maybe it's to let predators
know that you're poisonous.
Maybe it's to impress a mate.
Maybe it's because blue
pigment is so rare,
and evolving a way to fake blue
simply allows certain animals
to stand out from the crowd.
We don't yet know
why blue is so rare.
But the rarity of blue is
not just limited to animals.
Blue pigments are uncommon
everywhere in nature.
There are no blue foods.
Less than 10% of
flowers are blue.
And the two things
that most of us
think of as quintessentially
blue, the sky and the sea, also
only appear blue because of the
physics of light scattering.
NARRATOR: They say you
have to see something
with your own eyes
to believe it.
But nature shows that your
eyes are easily deceived.
We may not know why
blue is so rare,
but now we have to wonder, if
you can't trust your own eyes,
what can you trust?
