They're not camouflaging; they're expressing emotions!
Even though scientists avoid attributing human emotions to animals, the animal world was recently rocked with the true understanding of how a chameleon changes colors. Scientists already knew it had to do with their "emotional" state, but what happens on a microscopic level bewildered them.
While other color-changing animals like squid and octopus shift pigmented skin cells to alter their hue, chameleons use light reflection to go from green to rainbow. Their color-changing cells are called iridophores and microscopically shimmer with iridescence.
Nanocrystals inside these cells are arranged differently and come in unique shapes and sizes to aid in the structural reorganization that induces color change.
Scientists and professor Michel Milinkovitch of the University of Geneva in Switzerland explains how this color shift and light reflection works:
"When the skin is in the relaxed state, the nanocrystals in the iridophore cells are very close to each other -- hence, the cells specifically reflect short wavelengths, such as blue."
As the nanocrystals separate further away from each other, longer wavelengths of light, like yellows and reds, are reflected. Scientists are studying the chameleon's light reflection to see if they can use it in innovative technological designs that reduce light reflection, such as on shiny appliances.
Chameleons are typically calm in their leafy environment and so they remain a green color to blend in with their surroundings. But chameleons actually don't have green pigmentation. The nanocrystals are yellow. When they reflect light, the blue mixed with yellow gives the green appearance! However, in the presence of a female or male-male competition, their "emotional" state changes from calm to excited, resulting in bright, patterned colors.
It turns out the color change is more complex than scientists imagined. From nanoscience to emotions, it took a team of scientists from all different backgrounds to determine just how and why these brilliant, impressive creatures change colors.