The flag flown at Fort Mercer in 1777 was a variation of the Stripes With Union Of Stars in which the stripes were blue and white, while the canton was comprised of white, five-point stars on a red background.
Fort Mercer was constructed on the New Jersey side of the Delaware River, opposite Fort Mifflin.
There is no definite answer to the question of why the colors of the stripes and the canton are reversed
