A bunch of nonsense, of course, since there is no description in the book and they base their ideas on stuff written outside of Ms Austin's rural area: the styles seen as attractive in fashionable London.
"Our Mr Darcy portrayal reflects the male physique and common features at the time," says Amanda Vickery, professor of early modern history at Queen Mary University of London.
"Men sported powdered hair, had narrow jaws and muscular, defined legs were considered very attractive," she says.
uh, not really. The physique and facial shapes are based on genetics, so a better idea could be found among the pictures of her family:
or maybe pictures of Naval officers during the Napoleonic wars
as for powdered wigs, the reason for that was: Hair Lice. and the fad started because of baldness in King Louis XIV of France and the spotty hair loss from syphilis's that embarrassed people.
however, the claim that Mr Darcy should be envisioned as wearing a powdered wig may or may not be true:
Pride and Prejudice was written when Jane Austen was 21, i.e. 1796. So powdered wigs were still being worn then.
By the late 18th century, the trend was dying out. French citizens ousted the peruke during the Revolution, and Brits stopped wearing wigs after William Pitt levied a tax on hair powder in 1795. Short, natural hair became the new craze, and it would stay that way for another two centuries or so.