Prior to 1972, tennis balls were white believe it or not, and audiences watching from home tuned into the sport on black and white television sets. This meant that a white tennis ball stood out in greater contrast to the eye against the darker backdrop of a green grass court, a red clay or blue hard court surface. But, as a growing number of color television sets were entering homes around the world sports broadcasters noticed that audiences were having trouble picking out the ball on screen. So, in 1972, the powers that be decided that tennis balls should be switched to a new, brighter, more fluorescent color.
Researchers experimented with a whole host of different colors to see which ones were the most visible on color television, including bright orange and neon pink. Their results confirmed that the color 'optic yellow' was the most visible for TV audiences. After the study, the International Tennis Federation introduced yellow tennis balls into the official rules of the game. Surprisingly, it was not until 1986 that the All England Lawn Tennis Club (a.k.a. Wimbledon) switched to phosphorescent yellow balls. Long after the rest of the tennis world.
Jamie Reynolds of ESPN first worked at Wimbledon in 1980 and remembers the TV-unfriendly nature of the white balls. "They always turned green from grass stains," he recalls. "They blended so much with the grass the visuals were compromised. Remember, there was no HD then!" Summing it up, the dean of the ESPN tennis team, Hall of Famer and ESPN tennis commentator Cliff Drysdale, simply said, "I can't imagine playing without yellow balls."
So, now you know why tennis balls are yellow. It's not rocket science but, hey teaching your friends a history lesson about this will make you look pretty smart.