Jamie, the book doesn’t mention the Colfax Riot, but it does describe the New Orleans Riot of the following year on P. 123, in the Chapter, “Scalawags, the Lost Cause, and the Sunrise Attack Controversy”:

“During this period Longstreet’s public image plummeted still further, thanks to an outbreak of violence in Louisiana which sharply underscored his connection with the Radical Republicans. On September 14, 1874, the Crescent City White League attempted to overthrow Governor Kellogg’s administration by force of arms. As head of the militia, Longstreet led the state’s largely black troops against the insurgents, many of whom were Confederate veterans. In the ensuing street battle, the state militia broke and ran. One of the White League officers later wrote a friend, “It was with the greatest difficulty that I prevented the men from firing particularly at Longstreet. (59) Even so, Longstreet was wounded by a spent bullet and was captured by this foes, an experience which must have been the most humiliating of his life. Order was restored only at the intervention of federal troops." (60)

When I googled the Colfax Riot, the several items I scanned made no mention of Longstreet in that affair, so perhaps New Orleans 1874 is the one you were referring to?

Note References:

59: D.A.S. Vaught to John R. Ficklen, May 8, 1894, Ficklen Papers, LSU.

60: Sanger and Hay, “James Longstreet,” 370-71; Prichard, “Origins and Activities of the ‘White League’ in New Orleans, 530-32; 534-37; Taylor, “New Orleans and Reconstruction,” 203-04.