MLA

Simpson, Randolph Linsly, 1927-1992. Color by H.F. Gardner "Dr. King:" Martin Luther King, JR. seated in crowd; "March on Washington" button on lapel. Postcard in color. Box 25, folder 1036. circa 1970. https://collections.library.yale.edu/catalog/32312526.

APA, 6th edition

Simpson, Randolph Linsly, 1927-1992. (["Box 25, folder 1036"])(circa 1970)[Color by H.F. Gardner "Dr. King:" Martin Luther King, JR. seated in crowd; "March on Washington" button on lapel. Postcard in color]. https://collections.library.yale.edu/catalog/32312526.