English: Colour change and iridophore (kind of chromatophore) types in panther chameleons: these animals can rapidly change colour by modifying nanocrystals of guanine in iridophores in layers of their skin.

Captions:

(a) Reversible colour change is shown for two males (m1 and m2): during excitation (white arrows), background skin shifts from the baseline state (green) to yellow/orange and both vertical bars and horizontal mid-body stripe shift from blue to whitish (m1). Some animals (m2) have their blue vertical bars covered by red pigment cells.

(b) Red dots: time evolution in the CIE chromaticity chart of a third male with green skin in a high-resolution video; dashed white line: optical response in numerical simulations using a face-centred cubic (FCC) lattice of guanine crystals with lattice parameter indicated with black arrows.

(c) Haematoxylin and eosin staining of a cross-section of white skin showing the epidermis (ep) and the two thick layers of iridophores.

(d) TEM images of guanine nanocrystals in S-iridophores in the excited state and three-dimensional model of an FCC lattice (shown in two orientations).

(e) TEM image of guanine nanocrystals in D-iridophores.

Scale bars, 20 mm ( c); 200 nm (d,e).