In eighteenth-century America, most gentlemen wore carefully shaped white wigs, or powdered their hair to produce much the same look. I think only one hairstyle was more fashionably upper-class than wearing such a wig:
As Karin Calvert wrote in Of Consuming Interests:
In the privacy of his home or in an informal public setting, a gentleman removed his wig—which was hot, heavy, made the head itch, and could so cover the ears as seriously to impair hearing—and covered his shaved head with a soft nightcap. This was a cap commonly worn in the evenings and is not to be mistaken for a bedcap.Furthermore, wearing a cap instead of a wig signaled to other people that one was more interested in the life of the mind than in worldly concerns like crafts, business, and politics. And since only wealthy and genteel men could afford not to be interested in business, showing up in a cap demonstrated that one had reached the pinnacle of gentility.
Several gentlemen of the time had their portraits painted in their banyans (flowing robes, like dressing-gowns), nightcaps, and shaved heads. The John S. Copley painting above shows Nicholas Boylston, a wealthy Boston merchant who tilted toward the Whigs. (A larger scan of this image appears in the Wikipedia entry on banyans.) Boylston had his head shaved in order to wear a wig, but didn't wear his wig in this expensive portrait. Instead, his pose signals, he's more interested in the books under his left arm.
Nicholas's brother Thomas Boylston chose a similar approach for his Copley portrait. And here are two other portraits of gentlemen with shaved heads. When we imagine John and Abigail Adams at home in the 1760s and 1770s, discussing their children, politics, and books, we might have to think of John with his head shaved as clean as Curly Howard's.