“An investigation was in order. It began with the most obvious first stop, Wikipedia. “Tennis balls are fluorescent yellow at major sporting events, but in recreational play can be virtually any color,” the page for tennis balls said. And it’s true. A quick spin through Amazon shows that tennis balls, at least according to the labels, come in yellow and green and purple and even pink with Hello Kitty’s face on them.”

“Next, I turned to the official governing body of tennis around the world, the International Tennis Federation. According to the ITF, tennis balls were once actually white or black. The arrival of television changed that. Viewers had trouble seeing tennis balls as they hurled across the court in televised matches, so the ITF instructed tournaments to start using yellow ones in 1972 (though white ones were still allowed). The new rule said “the ball shall have a uniform outer surface consisting of a fabric cover and shall be white or yellow in color.” Cool history, but it didn’t help explain why we all felt completely unmoored from reason and reality.”

“Surely the suppliers of tennis balls could help. I reached out to a number of popular tennis-ball manufacturers, including Penn, Wilson, Dunlop, Gamma Sports, and Slazenger, as well as the sporting-goods stores Modell’s and Dick’s. Only Gamma Sports took my query seriously and responded. They put their answer in all caps: “OPTIC YELLOW!” (My colleagues who played tennis or had worked at tennis clubs—the ones with the most experience in actually looking at tennis balls—also thought they were yellow.)”