Green’s Dictionary of Slang

1. (also old blue) a swallowtail jacket, worn by black dandies.

1827		George Washington Dixon [song title] My Long-Tail Blue.
1839		‘Uncle Sam’s Peculiarities’ in Bentley’s Misc. 270: What a long-tailed blue dis nigga hab to be sure.
1841		‘The Long Tail Blue’ Dublin Comic Songster 25: I wears a jacket all the week, / And a Sunday my long tail blue.
1844		‘Jonathan Slick’ High Life in N.Y. I 196: I bundled up old blue, and the pepper and salt trousers.
1851		‘London Vocalists’ in Jolly Comic Songster 237: Dame Durden had five serving maids, with The long tail’d blue, sirs.
1860		London City Press 18 Feb. 5/5: [His] attire [...] consisting of a long-tail blue coat, knee breeches [...] and a yellow neckerchief.
1867		J. Greenwood Unsentimental Journeys 189: The various bands of Ethiopian ‘serenaders,’ many of whom, divested of their business as wool and ‘long-tail blues,’ mixed with the crowd.
1884		(con. c.1840) ‘Mark Twain’ Huckleberry Finn 161: He had an old long-tailed blue jeans coat with slick brass buttons flung over his arm.
1922		‘To Win A Yellow Girl’ in T.W. Talley Negro Folk Rhymes 102: You ‘borrow’ Mosser’s Beaver hat, / An’ slip on his Long-tailed Blue.
2001		(ref. to early 19C) N. Tosches Where Dead Voices Gather (ms.) 11: The long-tail blue was the swallowtail jacket emblematic of the wardrobe of urban black dandies — zip coons — of the early nineteenth century.

2. the black dandy that wore such a coat.

1839		‘Uncle Sam’s Peculiarities’ in Bentley’s Misc. 265: A dandy nigger, technically termed a ‘long-tailed blue,’ dancing Jim Crow’s pattern dance.
1844		Uncle Sam Peculiarities II 170: A dandy nigger, technically termed a ‘long-tailed blue,’ [is] dancing Jim Crow’s pattern dance [DA].
1867		Atlantic Monthly Nov. 610/2: ‘Clar de Kitchen’ soon appeared as a companion piece, followed speedily by ‘Lucy Long.’ [...] ‘Long-Tail Blue,’ and so on [DA].
1872		Schele De Vere Americanisms 153: [The song] Jim Crow [...] was quickly followed by several other songs of the same kind, such as Zip Coon, Longtailed Blue, Ole Virginny nebber tire, Settin’ on a Rail, etc.