At the US Open and other US-based tournaments, the men and women play with different tennis balls. The men play with the slower heavy-duty felt while the women play with the faster regular-duty felt. – WTF Fun Facts
Source: https://www.wsj.com/articles/at-u-s-open-do-women-play-with-faster-tennis-balls-11565957964
Tennis balls were originally white until Sir David Attenborough realized they’d be hard to follow on color television so the sport created “optic yellow” balls in 1972. Wimbledon didn’t allow them to be used until 1986. – WTF Fun Facts
Source: How tennis changed from white to yellow balls thanks to David Attenborough – Tennis365.com