Sometimes the most telling details can be gleaned from fiction:
Thrasher had rolled the single sheet of mimeographed paper into a child’s telescope and was sighting through it. Far below his office, clearly limned within the paper circle, he watched the summer visitors moving lazily about Rockefeller Plaza. The men wore white, yellow, and blue sport shirts without ties. Many of them wore cameras around their necks. The women were in pale, bulky frocks, patently different from the dark sleekness of dresses worn by the handful of native New Yorkers.Gerald Green, The Last Angry Man (1957)
Our protagonist, an advertising executive, notices the style differences between native New Yorkers and visiting tourists. And what better way to illustrate them than with a piece of 1950s advertising? Some of the female tourists no doubt made their own "pale, bulky frocks", hoping to look as pretty and as feminine as the women in the Wamsutta advertisement above.