This may actually be where I saw this claim - Proud Boys plan to protest incognito dressed as Antifa
The Proud Boys’ chairman, Enrique Tarrio, revealed on Parler that "the Proud Boys will turn out in record numbers on Jan 6th but, this time, with a twist. "The twist, Tarrio said, is that they will forgo their traditional uniform for something inconspicuous. He wrote: “We will not be wearing our traditional Black and Yellow.”
The group’s standard uniform is black and yellow Fred Perry polo shirts, military armor, and MAGA hats. Instead, the chairman explained: “We might dress in all BLACK for the occasion.” …The Proud Boys intend to take further steps to blend in with other protesters. Tarrio wrote: “We will be incognito and we will spread across downtown DC in smaller teams.”