Red is ripeness.

Red predominates in our perception; it’s a flag, a signal. There seems to be no topic or subject in human culture, even in nature, that is untouched by the meaning and making of red – as a color, as a symbol, as substance. At an edge of the rainbow, and somewhere opposite green, red burns into our retinas and somehow assumes prominence. Like sugar, it is the nature of red to call attention to itself. And like sugar, there’s a lot more red in modern life than nature paints.
Red, as a colorant, as a sugar, has become cheap. In a modern world of chemistry and pixels, the prestige of red suffers through abundance. That was not the case historically. Anciently, red was precious, the province of fruit, and flowers; blood, embers, and sunsets.

Where did that change start, and how did we arrive in the newer reality? The clue to both answers is verdancy. The light we see is limited to what our rainbow offers.***
Plants detect and utilize light outside our visible spectrum, employing far red light to measure daylength and and gauging ultraviolet light to avoid its damaging effects. Otherwise, their serious works is in our rainbow, selectively harvesting red and blue light for photosynthesis. We live in a verdent world because plants selectively absorb light from the red and blue bands of the rainbow, leaving green to reign. Our love of red might quickly boil down to the reality that we are surrounded by green.
'The Garden' What wondrous life is this I lead! Ripe apples drop about my head; The luscious clusters of the vine Upon my mouth do crush their wine; The nectarine and curious peach Into my hands themselves do reach; Stumbling on melons as I pass, Insnared with flowers, I fall on grass. Meanwhile the mind, from pleasure less, Withdraws into its happiness: The mind, that ocean where each kind Does straight its own resemblance find; Yet it creates, transcending these, Far other worlds, and other seas; Annihilating all that's made To a green thought in a green shade. Andrew Marvel, c. 1650

As the complement to green, red stands out. It is the apple in our eye.
That’s true for birds too. The normal purpose of a fruit is to produce seed that will go somewhere else, we call that dispersal. Birds are big-time consumers of fruit, and also active vectors (agents of dispersal, like wind and squirrels) for the real treasure, the seed. Watch the fruit in your garden; birds are watching too. As soon as certain fruit are ready for dispersal, the color changes from the green of growing to the red of ripeness, and the birds have at it. The fruit can be gone in a flash.

Flowering is dispersal also, but the trove to be moved is pollen. Anyone familiar with the habits of hummingbirds will key into the value of red as a cue. Birds see red selectively, and hummingbirds are particularly attentive, an advantage for flowers that can meet hummingbird standards.*
A Route of Evanescence, With a revolving Wheel – A Resonance of Emerald A Rush of Cochineal – And every Blossom on the Bush Adjusts it’s tumbled Head – The Mail from Tunis – probably, An easy Morning’s Ride – Emily Dickinson, on a Hummingbird

Red has been as important for humans as for birds; we’ve used it, historically, for splendor, celebration, caution… We take our cues, even measure progress through rubrics (red lettering), a practice derived from marking text to emphasize significance (such as the words of Christ), to guide ceremony, and (of course) to track change. Red was precious, in both sacrifice and celebration.

In pre-global, pre-industrial, pre-synthetic worlds, red was rare. Cave paintings used charcoals and rusty, earthen ochers (oxidized iron compounds hematites, that are the source of Venetian reds) to enliven images. Artisans around the globe learned increasingly to extract red dyes and pigments from many natural sources; among the more common were plants, such as madder (in Eurasia) and insects, including kermes (Mediterranean) and cochineal (in the neo-tropics).
The importance of color made extraction of usable dyes a driver in trade and alchemy, upscaling over time to exploitation and industry. Stories surrounding the signal significance of red (and scarlet, and crimson) in particular are often brazen and brutal. One colorant, we now know as carminic acid, is base for the brilliant Oaxacan cochineal, a hue of empire. **

The Huntington steeps in cochineal. Populations of the scale insect, Dactylopius confusus and perhaps other species, live on their obligate Opuntia hosts in all areas of the Gardens (we let them hang out because they are so incredibly fascinating). Amy Greenfield compiles the rich stories of cochineal in her 2004 book, A Perfect Red – Empire, Espionage, and the Quest for the Color of Desire, recounting the documented history of this natural product, accounts published in ancient texts that are a particular strength of Huntington Rare Books collections.
Alive with works contemporary to Shakespeare, Huntington collections include John Donne’s poetizing the role of cochineal in his young life (as Jack Donne) while on a pirating exploit led by Robert Devereux – the young earl of Essex who hauled 27 tons of red dye from Havana and had so charmed Queen Elizabeth as to keep the bulk of his booty. Fame and favor cannot last, as we learn the the earl’s daring led to his eventual beheading (an early romance reporting the story of Elizabeth and Devereux is also part of Rare Books: The secret history of the most renowned Q. Elizabeth and the E. of Essex, By a Person of Quality, 1680, #600805 )
Satyr IIII, Donne: The Ladies come; As Pirats, which doe know That there came weak ships fraught with Cutchannel (i.e. cochineal), The men board them; and praise, as they thinke, well, Their beauties; they the mens wits; Both are bought. Why good wits ne'r weare scarlet gownes, I thought This cause, These men, mens wits for speeches buy, And women buy all reds which scarlets die.
This is only one early tale. Cochineal remained mysterious for decades; people wondered, even wagered as to whether the granules that arrived in chests and barrels by the tens of thousands of pounds were animal, vegetable, or mineral. A rare book in the Library, Natuerlyke historie van de couchenille,… (#721627), published by Melchior de Ruusscher in 1729, recalls extreme documentation he assembled to verify the animal-sourcing of the dye, all done to claim a bet he made with a friend who denied that reality.
Ruusscher, however, held the advantage of having read Nicolaas Hartsoeker’s 1694 Essai de dioptrique (Huntington #481631), the first publication to clearly depict the insect making up grains of cochineal. Certainly Ruusscher’s friend was equally unaware that in 1704, Leeuwenhoek’s masterful illustrations of the insect were published in the Royal Society’s Philosophical Transactions.
The story continues to technicolor, with sagas of biopiracy. Daniel Rolander, a Linnaean disciple, managed to cop wild forms from Surinam in 1755, which he sent as living treasure to Linnaeus, insects only to be purged by the gardener, who was offended by the new pestilence in his hothouse. Rolander and the entire ordeal clabbered as a sour episode for Linnaeus, who wrote “About coccionella, I do not wish to speak, never wish to think or remember.” French patriot Nicolas-Joseph Thiéry de Menonville dedicated his life to bringing the dye under dominion (a story to which Greenfield gives a full 13 pages,) a narrative published post-mortem in Thiery’s Traité de la culture du nopal… (Huntington #721755.)
The inimitable botanist Joseph Banks, of course, had read Thiéry’s story and was swept into the cochineal drama, with the almost inevitable disastrous outcomes. Greenfield details Bank’s hopes; British domination with cochineal cultivation in India. At the end of 1795, the governor of Madras received “pieces of Cassimere cloth and Flannel, dyed with cochineal reared here, which in brightness and colour equal the best scarlets.” In short order, ecology and human culture put ends to what became a “resounding failure.” Similar tales bore similar fruit in Java, even in America.
Beginning with its ruby cousin madder, the red dye industry was soon transformed through the wonders of chemistry. By 1869, the first synthetic red (alizarin, the colorant in madder) was on the market, followed quickly by eosine, roccellie, and Biebrich scarlet. Even though carminic acid alluded synthesis until more recently, the other reds had it. Markets for cochineal and madder collapsed. Artificial red was, and remains, everywhere.

For contemporary life, that means urban and suburban scenes can be swamped with red, its impact diluted by billboards, storefronts, and banners. But in more natural settings, red remains restrained. Amazingly and happily, the abundance of red in commerce takes nothing away from nature’s reds, which never lose their attraction.
*I wonder if anyone has set up a trial in which red is added to the landscape gratuitously, to learn how that would impact success and behavior…. https://digitalcollections.sit.edu/isp_collection?utm_source=digitalcollections.sit.edu/isp_collection/2724&utm_medium=PDF&utm_campaign=PDFCoverPages
**Cochineal: A Bright Red Animal Dye, thesis of LaVerne M. Dutton, available at the website: http://www.cochineal.info/index.html
***The rainbow is slightly different for other animals. If I tell you about the birds and the bees, I have to reveal that both see into the UV spectrum, detecting light humans do not perceive.
References:
Greenfield, Amy Butler, 2004. A Perfect Red – Empire, Epionage, and the Quest for the Color of Desire
Donkin, R. A. “Spanish Red: An Ethnogeographical Study of Cochineal and the Opuntia Cactus.” Transactions of the American Philosophical Society, vol. 67, no. 5, 1977, pp. 1–84. JSTOR, http://www.jstor.org/stable/1006195. Accessed 12 Apr. 2020.
Roman Ulm and Gareth I Jenkins, 2015. Q&A: How do plants sense and respond to UV-B radiation? BMC Biol. 2015; 13: 45. Published online 2015 Jun 30. doi: 10.1186/s12915-015-0156-y PMCID: PMC4484705PMID: 26123292