The Australian chameleon grasshopper has the unusual property of changing color. At low temperatures, males are black. At temperatures above 25C, they turn a bright blue in a process that takes about 30 minutes. If the temperature is lowered to 10C, they revert to the black color in a process that takes 5 hours. How do they change color?
The epidermal cells of the male grasshoppers contain two types of granules. The larger granules are about 1 micron and contain light absorbing material. The smaller granules are 0.17 microns, contain pteridine and uric acid, and have optical properties of light scattering nanospheres. In the black form, the smaller and larger granules are homogeneously mixed in the cells. Light scattered by the smaller granules is absorbed by the larger granules, little light is reflected, and the result is a black color.
At 25C, the two types of granules separate. The smaller granules move to the apical third of the cell, and the larger granules are in the basal portion of the cell. In this configuration, a portion of the light in the blue wavelengths hits the small granules and is reflected. The reflected light produces a blue color. Other colors of light are scattered and absorbed.
Filshie and colleagues* placed some similar size (0.14 micron) polystyrene spheres on a microscope slide with black tape on the bottom. The polystyrene spheres had properties similar to the smaller granules; the black tape, the absorptive properties of larger granules. When placed on the slide as a thick solution, the polystyrene spheres appeared milky. However, as liquid evaporated and the film on the slide reduced to less than 200 micron thickness, a brilliant blue color was produced.
The blue color in Kosciuscola tristis is due to the physical structure and arrangement of the granules and not a pigment. Shifting the arrangement of granules shifts the color. This principal could be used in theory to make synthetic materials that change color.
*Filshie, B. K., Day, M. F. & Mercer, E. H. (1975). Colour and colour change in the grasshopper, Kosciuscola tristis. Journal of Insect Physiology 21, 1763–1770.