An Update

Since writing the study above, I came across two more images showing solid-colored wallpaper with gold borders. I include them here to offer a fuller picture of the possibilities available to the eighteenth-century homeowner. Most probably the first portrait was painted in England and the second in Germany. Wall treatments fashionable in Europe, such as those seen in these pictures, were adopted quickly in the United States.
Picture
A gentleman at breakfast, attributed to the English painter Henry Walton, ca. 1775–80. Toledo Museum of Art, 1956.77. The narrow gold border runs along the wainscoting and encircles the door. It would have bordered the top edge of the wall as well.
Picture
Johann Eckstein, Samels Family, 1788. Museum of Fine Arts Boston, 59.194, Ellen Kelleran Gardner Fund. Here, too, the upper edge of the wall is not visible, but we can see the decorative gold border just above the wainscoting. It is possible that the room was painted and stenciled rather than papered, but given the elegance of the carpet, the use of wallpaper seems more likely.
Copyright Margaret A. Oppenheimer, October 18, 2016