Although an ability to change colour has, in the natural world, long been traditionally associated with the chameleon, that reptile is by no means unusual in this regard. Other colour-changing animals include certain fish and frogs, cephalopods such as squid, and, if we include seasonal changes of fur, Arctic hares and foxes. There is no universal mechanism behind such properties — but understanding how they are attained, especially by creatures that can alter their appearance very rapidly, might offer valuable strategies for making materials that can adapt their passive light reflectance or transmission for applications ranging from display technologies to solar shielding and sensing techniques.

A different way to achieve coloration in animals is structural: wavelength-selective interference in rays reflected from ordered arrays of nanostructures. Nanopatterned wing scales, for example, create the startling blue iridescence of Morpho butterflies. Colour change might in this case be generated by altering the separation between the reflecting elements, as for example when the spacing of stacked plates of the protein reflectin in iridophores of squid is changed by a neurotransmitter-induced alteration of the electrical charge on the plates². As well as pigmented chromatophores, chameleons have iridophores containing guanine nanocrystals that act as wavelength-selective photonic crystals with tunable spacing, permitting colour variation across the spectrum³.

尽管变色龙在自然界中长期以来一直被认为具有变色能力，但这种爬行动物在这方面并不罕见。其他变色动物包括某些鱼类和青蛙、鱿鱼等头足类动物，如果考虑到皮毛的季节性变化，还包括北极兔和狐狸。这些特性背后并没有通用的机制，但了解它们是如何获得的，尤其是那些可以非常迅速地改变其外观的生物，可能会为制造能够适应其被动光反射或透射的材料提供有价值的策略，这些材料可以适应从显示技术到应用的各种应用。太阳能屏蔽和传感技术。

在动物中实现着色的另一种方法是结构性的：对从有序纳米结构阵列反射的光线进行波长选择性干涉。例如，纳米图案的翼鳞创造了大闪蝶令人惊叹的蓝色虹彩。在这种情况下，颜色变化可能是通过改变反射元件之间的间隔来产生的，例如，当乌贼虹膜细胞中蛋白质反射蛋白的堆叠板的间距因神经递质引起的板上电荷的改变而改变时² 。除了色素色素细胞外，变色龙还具有含有鸟嘌呤纳米晶体的虹色细胞，这些鸟嘌呤纳米晶体充当具有可调间距的波长选择性光子晶体，允许在整个光谱中发生颜色变化³ 。