The Obamas were loaned a selection of art from Washington area museums, including this piece by Glenn Ligon:
Glenn Ligon, Black Like Me #2, 1992, paint stick and acrylic gesso on canvas
See the New York Times slideshow since there doesn’t seem to be a large image available.
Update: here’s a larger image of a similar piece:
Glenn Ligon Untitled (I Do Not Always Feel Colored), 1990