How Chameleons Change Color? (2015)

Long projectile tongue, independently movable eyes and rapid color change. Chameleons are indeed very interesting animals (see the detailed account of Aristotle at the bottom of this post). Main video is a concatenation of all five supplementary materials associated with the a study demonstrating color change in Chameleons. You can view them individually below. The following video by The Economist makes a successful summary based on the same material:

Reproductively mature chameleon males rapidly switch on bold threatening colors when confronting another rival male. All this time the the leading hypothesis to explain this color change was that they may be moving pigments around in skin cells. A study by the University of Geneva researchers describes that chameleons change colors by rearranging an ordered array of nanocrystals in the top chromatophore (also known as iridophore) layer of skin cells. The tiny crystals in chromatophore cells are made from guanine, one of the nucleic acid building blocks of DNA.

The nanocrystals in chromatophores strongly reflect one color of light, such as green when in relaxed state. Green color helps chameleons to blend themselves in the background. When a rival male is detected in vicinity, the animals stretch their skin cells which broadens the nanocrystalline lattice. In this excited state the crystals reflect a longer wavelength of light, such as yellow. Researchers also found that chameleons contain a second, deeper layer of chromatophores that reflect infrared light. Absorbance of infrared light can increase body temperature. Reflectance of infrared light may be helping the animals avoid excessive heating.

Biomimetics and bionics are the science of imitation of nature for solving human problems. Understanding chameleon color change biology could help design new materials that change colors when stretched.

Excitation color change sped up 8 times:

Relaxation color change sped up 8 times:

Excitation color change sped up 3 times:

Single cell color change sped up 30 times:

Simulated colors at the Brillouin zone during lattice compression:

In his treatise Historia Animalium Aristotle gives a detailed account of his observations from the Mediterranean chameleon:

“The chameleon resembles the lizard in the general configuration of
its body, but the ribs stretch downwards and meet together under the
belly as is the case with fishes, and the spine sticks up as with
the fish. Its face resembles that of the baboon. Its tail is exceedingly
long, terminates in a sharp point, and is for the most part coiled
up, like a strap of leather. It stands higher off the ground than
the lizard, but the flexure of the legs is the same in both creatures.
Each of its feet is divided into two parts, which bear the same relation
to one another that the thumb and the rest of the hand bear to one
another in man. Each of these parts is for a short distance divided
after a fashion into toes; on the front feet the inside part is divided
into three and the outside into two, on the hind feet the inside part
into two and the outside into three; it has claws also on these parts
resembling those of birds of prey. Its body is rough all over, like
that of the crocodile. Its eyes are situated in a hollow recess, and
are very large and round, and are enveloped in a skin resembling that
which covers the entire body; and in the middle a slight aperture
is left for vision, through which the animal sees, for it never covers
up this aperture with the cutaneous envelope. It keeps twisting its
eyes round and shifting its line of vision in every direction, and
thus contrives to get a sight of any object that it wants to see.
The change in its colour takes place when it is inflated with air;
it is then black, not unlike the crocodile, or green like the lizard
but black-spotted like the pard. This change of colour takes place
over the whole body alike, for the eyes and the tail come alike under
its influence. In its movements it is very sluggish, like the tortoise.
It assumes a greenish hue in dying, and retains this hue after death.
It resembles the lizard in the position of the oesophagus and the
windpipe. It has no flesh anywhere except a few scraps of flesh on
the head and on the jaws and near to the root of the tail. It has
blood only round about the heart, the eyes, the region above the heart,
and in all the veins extending from these parts; and in all these
there is but little blood after all. The brain is situated a little
above the eyes, but connected with them. When the outer skin is drawn
aside from off the eye, a something is found surrounding the eye,
that gleams through like a thin ring of copper. Membranes extend well
nigh over its entire frame, numerous and strong, and surpassing in
respect of number and relative strength those found in any other animal.
After being cut open along its entire length it continues to breathe
for a considerable time; a very slight motion goes on in the region
of the heart, and, while contraction is especially manifested in the
neighbourhood of the ribs, a similar motion is more or less discernible
over the whole body. It has no spleen visible. It hibernates, like
the lizard.”