The English word chameleon (/kəˈmiːliən/ kuh-MEEL-ee-un, /kəˈmil.jən/ kuh-MEEL-yuhn) is a simplified spelling of Latin chamaeleōn, a borrowing of the Greek χαμαιλέων (khamailéōn), a compound of χαμαί (khamaí) "on the ground" and λέων (léōn) "lion".

In 1986, the family Chamaeleonidae was divided into two subfamilies, Brookesiinae and Chamaeleoninae. Under this classification, Brookesiinae included the genera Brookesia and Rhampholeon, as well as the genera later split off from them (Palleon and Rieppeleon), while Chamaeleoninae included the genera Bradypodion, Calumma, Chamaeleo, Furcifer and Trioceros, as well as the genera later split off from them (Archaius, Nadzikambia and Kinyongia). Since that time, however, the validity of this subfamily designation has been the subject of much debate, although most phylogenetic studies support the notion that the pygmy chameleons of the subfamily Brookesiinae are not a monophyletic group.

While some authorities have previously preferred to use this subfamilial classification on the basis of the absence of evidence principle, these authorities later abandoned this subfamilial division, no longer recognizing any subfamilies with the family Chamaeleonidae.

In 2015, however, Glaw reworked the subfamilial division by placing only the genera Brookesia and Palleon within the Brookesiinae subfamily, with all other genera being placed in Chamaeleoninae.

Some chameleon species are able to change their skin coloration. Different chameleon species are able to vary their colouration and pattern through combinations of pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise, and purple. Chameleon skin has a superficial layer which contains pigments, and under the layer are cells with very small (nanoscale) guanine crystals. Chameleons change colour by "actively tuning the photonic response of a lattice of small guanine nanocrystals in the s-iridophores". This tuning, by an unknown molecular mechanism, changes the wavelength of light reflected off the crystals which changes the colour of the skin. The colour change was duplicated ex vivo by modifying the osmolarity of pieces of white skin.

Colour change in chameleons has functions in camouflage, but most commonly in social signaling and in reactions to temperature and other conditions. The relative importance of these functions varies with the circumstances, as well as the species. Colour change signals a chameleon's physiological condition and intentions to other chameleons. Because chameleons are ectothermic, another reason why they change colour is to regulate their body temperatures, either to a darker colour to absorb light and heat to raise their temperature, or to a lighter colour to reflect light and heat, thereby either stabilizing or lowering their body temperature. Chameleons tend to show brighter colours when displaying aggression to other chameleons, and darker colours when they submit or "give up". Most chameleon genera (exceptions are Chamaeleo, Rhampholeon and Rieppeleon) have blue fluorescence in a species specific pattern in their skull tubercles and in Brookesia there is also some in tubercles on the body. The fluorescence is derived from bones that only are covered in very thin skin and it possibly serves a signaling role, especially in shaded habitats.

Some species, such as Smith's dwarf chameleon and several others in the genus Bradypodion, adjust their colours for camouflage depending on the vision of the specific predator species (for example, bird or snake) by which they are being threatened. In the introduced Hawaiian population of Jackson's chameleon, conspicuous colour changes that are used for communication between chameleons have increased whereas anti-predator camouflage colour changes have decreased relative to the native source population in Kenya where there are more predators.

Chameleons have two superimposed layers within their skin that control their colour and thermoregulation. The top layer contains a lattice of guanine nanocrystals, and by exciting this lattice the spacing between the nanocrystals can be manipulated, which in turn affects which wavelengths of light …

Read more on Wikipedia