The spread and fear of small pox, combining with the crowding of the city, produced much discussion of this subject in the winter of 1862-'63. In "Richmond at War," Louis Manarin's 1966 editing of the minutes of the city council (UNC Press), at page 261 (12 Jan 1863), the use of the white flag is required. The flag was to be "not less than twelve inches square." (The penalty was five dollars for each day the flag was not shown.)
Thanks for picking up the newspaper note, for I had missed this in the book.