Blue is a rarity among plants and animals. When it does occur in nature, it often isn’t truly blue, but rather a trick of diffraction, or the scattering of light, which is the case for bird feathers, sky, ice, water and iridescent butterfly wings. ... In response to growing pressure from consumers across the globe, Mars announced in February that over the next five years it would remove artificial colors from all the processed foods it makes for human consumption, and that pigments found in natural substances would take their place. ... In 2013, the Food and Drug Administration approved Mars’s petition to use the microscopic algae spirulina to make the first natural blue dye approved for use in the United States. As a result, any food manufacturer in the country can legally use spirulina as a colorant. Mars spent years researching spirulina’s safety; in order to overhaul 1,700 or so recipes and update its global manufacturing capabilities, the company desperately needs a substitute for synthetic Blue No. 1, as does the rest of the industry. But right now, there isn’t nearly enough spirulina dye to go around — and in any case, sometimes it doesn’t yield just the right blue, or the color degrades and comes out blotchy, or it tastes odd. ... Humans are color-seeking animals, and food companies learned to manipulate that trait early. ... One Mars executive told me that to convert only its blue M&Ms to spirulina blue, the company would, in his estimation, need twice the current global supply. ... last year the global market in natural colors was worth an estimated $970 million, up 60 percent since 2011. Natural colors now represent more than half the food-colors market in dollar terms.

Under Cheng, Didi has expanded in just four years to 400 Chinese cities. The service lets users digitally hail and pay for taxis, private cars, limousines, and commuter buses. Cheng says 80 percent of all taxi drivers in China now use Didi to find passengers. So many people use the app, it can be difficult to get a cab during rush hour without it. Investors recently valued Didi at $35 billion, making it one of the most valuable private companies in the world. Uber, with operations in almost 500 cities on six continents, is worth $68 billion. ... Cheng was born in Jiangxi province, a landlocked region in eastern China famous for being the cradle of Mao Zedong’s Communist revolution. His father was a civil servant, his mother a mathematics teacher. He says he excelled at math in high school but during his college entrance exams neglected to turn over the last page of the test, leaving three questions blank. He got into the Beijing University of Chemical Technology, less prestigious than the upper-echelon schools. ... it turned out that Didi had a few advantages over the competition. Some were copying Uber’s U.S. strategy of working with limousine and town car chauffeurs. But there are far fewer black cars than yellow cabs in China. ... Instead of imitating competitors and giving away smartphones to drivers, an expensive proposition for a capital-strapped startup, they focused on providing their free app to younger drivers who already had phones and were likely to spread the word about Didi.

Is there a workable business model for products that are built to last, rather than to fall apart? This is an idea that I explored here in July, in a story about the L.E.D. quandary. That quandary, in short: companies are making a good thing—light-emitting-diode bulbs that conserve energy and last for years—but they can’t make money in the long run from products that rarely need replacing. As global light sockets fill with L.E.D.s, century-old corporate titans are getting out of the bulb business even before “socket saturation” tips sales into a decline. The question remains whether any company has an incentive to make a product that is not designed to fall apart or become obsolete.

Harry Potter brought the philosopher’s stone back as a cultural reference point, but the idea of a universal panacea against death is much older than J.K. Rowling. From Alexander the Great to Ponce de León, tales of conquistadors and rovers stumbling onto fountains of youth are a fable trope. Greek mythology addressed the horror of aging in the tale of pitiful Tithonus, kidnapped by the goddess Eos and granted eternal life. Eos f***ed up and forgot to specify that Tithonus should stay young as well as living, and so her kidnapped boy toy aged into a trembling old man, lasting on and on in babbling, incapacitated misery. In some versions of the story he turns into a cicada, but the moral remains: Eternal life without eternal youth is a curse, which is why RAAD wants both. ... The people who organized RAAD are members of the Coalition for Radical Life Extension, which is the nonprofit offshoot of People Unlimited, a Scottsdale, Arizona–based group that describes itself as “a community of people living physical immortality.” People Unlimited charges a $245 monthly membership fee, and holds regular meetings where members swap antiaging tips and listen to guest speakers. Many of the presenters at RAAD are also members or guest speakers at People Unlimited. ... The coalition’s online mission statement shoehorns immortality into a historical narrative of moral and social progress. ... “Asked whether they, personally, would choose to undergo medical treatments to slow the aging process and live to be 120 or more, a majority of U.S. adults (56%) say ‘no.’” The study also found that around half the people questioned had never heard of radical life extension; around half also answered that it would be bad for society.

With greater oil reserves than Saudi Arabia, Venezuela should be at least moderately prosperous. Instead, it has the world’s fastest contracting economy, the second highest murder rate, inflation heading towards 1,000% and shortages of food and medicine that have pushed the poorest members of its 30 million population to the edge of a humanitarian abyss. ... It takes just five minutes to cross from the porous border at Pacaraima. Locals say the government in Caracas lifted food import tariffs from Brazil two months ago in a sign both of its desperation to ease shortages and its weakening control over the economy. There is now a steady stream of traders buying sacks of rice, sugar, wheat and spaghetti for resale in Venezuela. ... Life could be made easier if the authorities printed notes with higher denominations than 100 Bolivars, which is worth less than 8p, or 10 cents. But the central bank appears reluctant to make a move that would confirm a level of hyperinflation not seen in Latin America since the crises in Brazil and Argentina in the 1980s and 1990s. As a result, locals have to pay for everything in the equivalent of dimes. Even when made of paper, that can be cumbersome and heavy. ... The government’s tendency to subsidise many products below the cost of production is a major reason why the economy is in such a mess. ... Even in the midst of crisis, the government still hands out free or massively discounted homes, cars, DVD players and microwave ovens.