Why 11 well-known yellow things are yellow

In 1920 roads were becoming more crowded and more dangerous, so Detroit police officer William Potts converted railroad signal lights into the first traffic light. Railroad lights were initially white, green, and red, but in the early 1900s, yellow replaced white because it was deemed more visible.

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The business phone book owes its distinctive colour to a printer in Cheyenne, Wyoming, which in 1883 ran out of white paper while printing one of the first ever phone directories (the phone had only been patented a few years earlier). So the printer finished the job on yellow paper, and it caught on.

In 1915 Chicago businessman John Hertz founded the Yellow Cab Company. He commissioned a university study to “scientifically ascertain which colour would stand out strongest at a distance.” The winner, of course, was yellow. But Hertz wasn’t the first: In 1909 Albert Rockwell operated a fleet of yellow cabs in New York City. He wasn’t as scientific, though – he chose yellow because it was his wife’s favourite colour.

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In the 1890s, Joseph Pulitzer’s New York World was among the first newspapers to use sensationalism and hyperbole to sell issues. One of the World’s comic strips, “Hogan’s Alley” by Richard F. Outcault, featured a popular character called the Yellow Kid. When William Randolph Hearst launched the rival New York Journal, he hired Outcault away from the World. Pulitzer vowed revenge: He hired a new cartoonist to create a second Yellow Kid, and as the two newspapers traded barbs back and forth, their style of over-the-top reporting came to be known as ”yellow journalism.”

A banana starts out green because its peel contains chlorophyll, like any other green plant. As the fruit ripens, a chemical reaction in the peel causes the chlorophyll to break down. As the chlorophyll level drops, the green fades, and the banana turns yellow.

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An early 20th-century folk tale tells of a convict returning home – if his family welcomed him, they would tie a white ribbon around an apple tree. In 1971 New York Post writer Pete Hamill penned a dramatic retelling–except in the version he’d heard, the ribbon was yellow and the tree was oak. That article inspired an ABC TV movie and then a song composed by Irwin Levine and L. Russell Brown called “Tie a Yellow Ribbon Round the Old Oak Tree.” It became a huge hit for Tony Orlando in 1973. The ribbon got its modern meaning –remembering the military – during the 1980 Iran Hostage Crisis when Penne Laingen, wife of the captive US ambassador Bruce Laingen, told the Washington Post that she tied a ribbon around a tree in her yard: “One of these days, Bruce is going to come home and untie that yellow ribbon.” (He did.)

The Huang He, or “Yellow River,” is the second-longest river in China (3,395 miles,) and the seventh-longest in the world. It was named for the billions of tons of yellow silt that it carries.

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When your body replaces red blood cells, it creates bilirubin, which is yellow. The liver normally removes bilirubin, but when a baby is in utero, the placenta removes it. When the baby is born, the liver doesn’t always start filtering immediately. Result: bilirubin causes a yellowing of the skin and eyes. Called physiological jaundice, the baby is yellowest at two to four days old. Although this type of jaundice can look alarming, it’s usually harmless. (But it should be checked by a doctor.)

In the annual Tour de France bicycle race, the leader at the start of each stage wears le maillot jaune, or “yellow jersey.” The race itself dates to the turn of the 20th century, but the yellow jersey made its first appearance in 1919 to make the leader more conspicuous. Why yellow? Because a magazine called L’Auto sponsored the race, and it was printed on yellow paper.

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The sun is yellow, right? Wrong. It’s white. Why white? Because sunlight contains all the colours of the spectrum. But the photons that come from the sun are mostly in the green spectrum. So if the sun is white, and most of its photons are green, how do we see it as yellow? Earth’s atmosphere is to blame: Red, yellow, and orange aren’t scattered as easily as the rest of the spectrum, so when sunlight is filtered through the atmosphere, those are the colours that we see.