The tennis courts at Furman Park have been closed for resurfacing for a couple of weeks now. I didn't see much progress until the last couple of days, when the colors were added.
Concrete courts such as this one used to be painted in colors to mimic natural courts: brick red to mimic the clay of the outer court, and grass green for the inner court. The courts here at the park, originally built in 1970, used those same colors.
But most pro courts are now blue. Initially, the trend may have started as a mere marketing gimmick, a way of branding a particular tournament. But players and TV producers alike soon discovered that blue (and purple) created a lot more contrast against the yellow tennis balls. So what started out as a fashion statement soon turned into a win-win situation for everyone.
And that, I assume, is why the Furman Park tennis courts are now a bright blue.