Tennis balls are 'Optic Yellow' because this color is the easiest for television viewers to track.

The transition from white to fluorescent yellow tennis balls was driven by the limitations of early color television technology. In the late 1960s, David Attenborough was the controller of BBC2 and oversaw the introduction of color broadcasts in the UK. He noticed that white tennis balls often disappeared on screen, especially when they moved in front of white clothing or bright stadium lights. This led to a search for a color that would provide maximum contrast for both home viewers and live spectators.The specific shade chosen is officially known as 'Optic Yellow' or fluorescent yellow-green. This color sits at a wavelength of approximately 555 nanometers, which is the peak sensitivity of the human eye's cone cells during daylight. Scientific studies conducted in the early 1970s confirmed that this specific hue is the most visible against various backgrounds, including green grass and clay courts. The high visibility is crucial because a professional tennis serve can exceed 140 mph, making tracking difficult for the human brain.The International Tennis Federation (ITF) officially introduced yellow balls into the rules of tennis in 1972. Despite the clear visibility benefits, traditionalist institutions were slow to adopt the change. The Wimbledon Championships continued to use white balls for another 14 years, finally making the permanent switch to yellow in 1986. Today, the ITF maintains strict regulations on the exact shade and reflectivity of the felt to ensure consistent visibility across all global broadcasts.