Blue barely describes a jay’s feathers: the soft ozone blue of its crest and mantle, the jewel-toned panes - lapis, sapphire, turquoise - of its tail and wings. Blue is scarcely adequate to
explain the subtly mingled tones of a wild blue phlox flower - pink into lavender into
periwinkle; or the deep magentas and violets of a great blue lobelia.
As a watercolorist, I’m fascinated by colors, their histories and properties. As a naturalist, I find the color blue especially intriguing, not just because it’s sublime to stroll along a creek bank thick with Virginia bluebells or to be dazzled by the iridescent flash of a male bluebird, but because blue is relatively uncommon in nature, and the differing ways animals and flowers create blue is remarkable.
The blue of a jay, indigo bunting or bluebird—or a pipevine swallowtail, a juvenile skink’s tail, the eyes of a bobcat kitten—are created not by pigments but by structural elements in the animals’ feathers, scales or irises. Animals produce black and a wide range of grays and browns with the pigment melanin. Some also metabolize the food they eat to create bright reds and yellows. But animals are unable to produce blue pigment.
The animal blues we perceive are a result of light striking stacks of clear, layered
nanostructures in the barbules of a feather or the surface of a scale, bouncing around and
interacting with underlying pigments, interfering with other wavelengths, and reflecting back to our eyes as blue. The quality of blueness depends on the angle of the light; this is why
bluebirds appear gray in poor light and buntings nearly black, and accounts for the brilliance of their plumage in the sun.
Animals create green through mixing structural blue with yellow pigments absorbed and
modified from plant foods. When the production of yellow goes awry, the structural blue color persists –and the discovery of a bright blue leopard frog might make the news. When a green snake dies, its yellow pigment fades, leaving the overlying structural color that is unaffected by metabolism—and after death the green snake turns blue.
Other organisms neither plant nor animal, such as the indigo milky mushroom found in our oak forests, make blue by alternative chemical means. This fungus exudes a lustrous indigo latex when broken or bruised, a color derived from azulene, an organic compound present in the mushroom and an isomer of naphthalene. (The indigo milky is edible, and although it turns to brown when cooked, there are ways of preserving its color just enough to create an unworldly teal green sauté).
I am not alone in my particular fondness for blue flowers. Two biotech companies on two
continents worked for over a decade to genetically engineer a “blue rose”—which, despite the hype, turned out. . . dull purple.
Naturally “blue” flowers are anything but dull, but rarely attain a pure blue; wildflowers are nearly always lavender, violet or blue that appears on the verge of slip-sliding into pink.
Flowers create many biological pigments, among them anthocyanins. Anthocyanins are the pigments that make leaves and fruits turn bright red in autumn, and their “sugar free” counterparts are anthocyanidins, named for the flowers from which they were originally isolated. These pigments make pink and red in rose petals (cyanidin, the first isolated anthocyanidin), geraniums (pelargonidin), peonies (peonidin), petunias (petunidin) and mallows (malvidin).
There is no purely blue stand-alone pigment in flowers, but another anthocyanidin, delphinidin, after Delphinium, is found not only in larkspurs, but violets and other blueish flowers. The pink and red pigment-anthocyanidins are also present in blue flowers and play their part in creating all those purplish hues.
Making blue is a complex process of combining delphinidin with other elements present
in the plant, such as calcium, glucose, acids and various metals. The blueness of a flower is also affected by pH. Aluminum is employed by hydrangeas to make blue flowers, for instance, but the aluminum naturally present in soil isn’t available for absorption by the plant unless the soil is sufficiently acidic. So here in the limy Midwest, the soil must be acidified with sulfur or vinegar—otherwise pink petals will prevail.
The default for hydrangeas is white, of course, and it's not uncommon to find "blue" wildflowers--such as larkspurs, violets, bluebells and phlox--that are pale or even pure white, the alchemy to create blue having been skewed by some internal glitch or external anomaly.
Many flowers rely on animals for pollination and dissemination, and blue is a color most
animals can see. Blue fruits, especially accentuated with magenta stems, attract birds and
mammals to serve as seed-distributors. Bees see best in the pink and blue spectrum, and in addition to using clever chemistry to create blues, flowers communicate with bees through the slippage of pink into blue and vice-versa.
Metabolic processes, such as pollination and fertilization, affect the pH inside flowers. Blue flowers in the borage family, including garden borage and comfrey and our native Virginia Bluebells, are pink in bud. When fully developed and ready for pollination, they take on their blue hues, signaling to bees that they’re open for business. Lupines, on the other hand, often change from violet-blue to pink after pollination, cuing bees on where - and where not - to concentrate their efforts.
Flowers also have structural color like birds, creating iridescent areas on petals that may act as nectar guides for insects. And beyond blue--is ultraviolet, hidden from the human eye. But after all, flowers aim their colors at pollinators, not people, and birds are all about attracting a mate. We humans are the lucky, if unintended, admirers and cultivators of nature’s breath-taking blues.