These color changing morphs are triggered not by color change in their environment, but a change in background brightness. This type of environmental change would be caused by seasonal fluctuation. A full change in the dorsal coloration of a color morph can take anywhere from weeks to months, but initial changes can occur in just a few hours. This has been shown to be a very useful cryptic survival feature for these frogs.
Skin color is produced via pigment cells called chromatophores. There are commonly three types of chromatophores found in amphibians: 1. Xanthophores - These contain yellow, orange, or red pigments and are found uppermost on the dermis; 2. Iridophores - These lie below the xanthophores and function by reflecting and scattering white light up through them; in the case of Pseudacris regilla and many other North American frogs, iridophores reflect blue light through the yellow pigment cells above to create a green frog; 3. Melanophores - These are the deepest pigment cells and are responsible for the presence of black and brown pigments.
Photographed at the vernal pools at Madrona Marsh, Torrance CA: www.friendsofmadronamarsh.com
Hand-held D5000 at ISO 400, 1/200-sec at f/22, partial shade & Nikon SB-600 speedlight with O-Flash 3/4-circle Fresnel prism attachment. Approx 1:2 mag. (1/2 life-size): the size of your fingernail.