Jeu de palme players at a country palace. Adriaen van de Venne, 1614
While such restrictive clothing no doubt taxed the Nadals and Federers of old, still the game spread across Europe. When tennis-like games came to the United States in the 18th and 19th centuries, rich Americans too played in their day clothes, and were, you can imagine, a little uncomfortable doing so.
It's fair to say that, around the turn of the 20th century, a game very much like contemporary tennis had developed and become a sport. But even then the dictates of modesty prevailed over those of performance—especially for women. Through the end of the 19th century, young ladies wore full bustles, dress hats, and gloves on the court.
Nonetheless, this era saw the first tennis tournament. And, eventually, practicality won out. Competitive tennis called for new outfits. It called for tennis whites!
Library of Congress
By about this time, the rich in America (and England) had adopted summer white as a symbol of their leisure. Since white clothing dirties easily, it didn't recommend itself to factory workers and domestic servants in a dry-cleaning-less era of weekly baths. In fact, really the only people suited to wear white were people who didn't work at all—or who could at least afford to look like they didn't.
Library of Congress
Wearing white cost a lot. If you wore it, you signaled that you, too, cost a lot. Since tennis had long been a summer game for the rich, the rich wore white to play tennis. And—since the middle class likes to imitate the rich—as tennis democratized over the course of the 20th century, the middle class wore white to play, too.
Gradually, white for tennis became a rule, so that in 1890 Wimbledon mandated all-white outfits for players. Elsewhere, the all-white tennis outfit became a decorous standard by the early 20th century—just in time, by the way, for the Frenchwoman Suzanne Lenglen to aggravate rich people everywhere by playing tennis in a (white) calf-length skirt and short sleeves.
Lenglen at play, shot by Jacques-Henri Lartigue, 1921
American flappers, however, saw no problem with this. As general hemlines rose, so too—and faster still—did the hemline of the tennis skirt. American Gussie Moran wore an above-the-knee skirt to compete at Wimbledon in 1949. Her ruffled white underwear showed with every movement, and photographers lay on the ground in order to best capture it. (As usual, men faced easier fashion choices. They began to wear white around the same time as women, but their move from pants to shorts over the first half of the 20th century made little stir.)
Unlucky Gussie. She was embarrassed, but a decade or so later, her short skirt was old news. We had reached the age of the white and the short, and most female athletes thought nothing of bearing their underwear while they played—or of wearing shorts instead. (Helen Jacobs was very first to do so at a major match, in 1933.) Over time, today's tennis whites became the standard outfit. Tight and colorful aberrances in the 1980s and early '90s met appropriate outrage.