Because you wondered why tennis balls are yellow:

The answer lies with Sir David Attenborough. In the 1970s, as a BBC2 controller transitioning broadcasts from black and white to color, Attenborough noticed that white tennis balls were hard to see on TV against the white court lines. To solve this, he championed the switch to yellow balls, which were more visible on color televisions. Thanks to his insight, yellow tennis balls became standard by 1986, even at Wimbledon, and have remained the norm ever since.

More here.