There’s a misconception that chameleons change their color to blend in to their surroundings but research shows the opposite is true. In fact, chameleons’ baseline color (shades of green or brown) is camouflage and they naturally blend in.
It’s when they want to express themselves (e.g., feeling threatened or annoyed) that they dramatically change their color. The secret are iridophores, a layer of cells just beneath the chameleon’s skin. Iridophores are salt crystals made from guanine that are less than 1/100th the width of a human hair. And the faster they change their color, the more excited they are.
KQED, the PBS station in San Francisco, recently produced a segment delving into chameleons color-changing ways for their 4K YouTube series Deep Look.
You can check out the video embedded below as well as find a collection of stills and gifs from the segment, graciously provided by the KQED team.
Scientists used to believe that chameleons changed color by spreading out pigments in their skin, much like octopuses or squid do. The top layer of chameleon skin – called the epidermis – contains yellow pigment cells called xanthophores, and red pigment cells called erythrophores. But the amount of pigment in the cells stays the same, even when the chameleon changes color. [source]
Just beneath the chameleon’s skin is a layer of cells called iridophores. These cells contain microscopic salt crystals, which are arranged in a three-dimensional pattern like oranges stacked on a fruit stand. [source]
When light hits the crystals, some wavelengths are absorbed and some are reflected. The result, to our eyes, is the beautiful rainbow of colors on the chameleon’s skin. But what we’re actually seeing is light that is bouncing off of these tiny crystals. [source]
What we perceive as green, for example, is blue wavelengths of light being reflected off the crystals and through the layer of yellow xanthophore cells in the chameleon’s epidermis. The result is bright green skin that contains no green pigment. The process of changing color is called metachrosis. [source]