Skin deep
We all know that chameleons can change colour – these remarkable reptiles can alter their appearance in a split second in order to send signals to others or blend into their background. But how do they do it? The answer lies in specialised cells, called chromatophores, found in layers under their transparent outer skin. Those in the upper layer contain yellow and red pigments; those in the next layer down are strong reflectors of blue light; and those at the bottom contain dark melanin, and can open or close in order to concentrate or disperse their pigment granules. By manipulating this bottom layer, the chameleon determines the intensity of reflected light passing through the layers above and thus mixes colours like paint on a palette.

Light show
Bright colours may seem pretty pointless after dark – and, indeed, the subtle tones of most nocturnal creatures are adapted more for camouflage by day. Fireflies, however, can produce a colour that shines through the darkness. The eerie blue-green glow of these winged beetles and their larvae (glow-worms) is known as bioluminescence. It is a ‘cold light’, created by a chemical reaction in special organs on the lower abdomen, and generates no heat energy. Adult fireflies flash their lights to attract mates while larvae use them to deter predators. Bioluminescence is also widespread among marine organisms, from corals to squid, with some deep-sea fish also producing yellow, red and infrared lights.

Pretty in pink
Ever noticed how hippos seem to get pinker as the day goes on? The rosy flush that suffuses the naked skin of these heavyweight herbivores is due to an oily secretion that they produce when exposed to intense sunlight. Colourless to begin with, but quickly turning red, this gooey substance – more like mucus than sweat – acts as a sunscreen and helps to cool the animal. It contains two pigments, hipposudoric acid (red) and norhipposudoric acid (orange), which absorb ultraviolet radiation and scatter the light. Hipposudoric acid is also strongly anti-bacterial, which may explain why hippos’ numerous cuts and wounds – the result of their territorial skirmishes – seldom become infected.

Black cat on a dark night
Black panthers are not a species in their own right but simply leopards with an excess of the dark pigment melanin. Look closer and you can clearly see the familiar pattern of spots and rosettes, like printed silk, beneath the dark fur. This inherited trait – the result of a recessive gene – is thought to confer an evolutionary advantage to individuals that live in dark forests, enabling them better to stalk their prey. Though common in parts of Southeast Asia, black leopards are rare in Africa. However, they have been recorded in Cameroon, on the slopes of Mount Kenya and – especially – the dense forests of the Ethiopian Highlands, where as many as one in five may be melanistic.

Tricks of the light
The superb starling of east Africa is resplendent in its feathered finery, but its vivid colours are not all produced in the same way. The red-orange of the belly feathers is pigmentation – specifically pigments called carotenoids, originally produced by plants, which birds absorb through their diet. The dazzling blues, greens and violets of the breast and upperparts are, by contrast, ‘structural’ colours: just like the blues and greens of kingfishers, rollers and other iridescent species, they are produced by the refraction and reflection of light through tiny prisms in the feather barbs. Thus the beauty of these birds really is in the eye of the beholder.