Green’s Dictionary of Slang

(a) gin, esp. second-rate gin.

1755		Connoisseur No. 53 n.p.: Madam Gin has been christened by as many names as a German princess: every petty chandler’s shop will sell you sky-blue [F&H].
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions .
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn) n.p.: Sky Blue. Gin.
1802		Sporting Mag. Nov. XXI 82/1: His friends [...] were regaling each other with sky-blue and whisky.
1811		Lex. Balatronicum.
1821		‘An Amateur’ Real Life in London I 394: The Painter considers it desirable to produce effect by mingling his dead white with a little sky blue.
1833		T. Hood ‘Ode to Admiral Gambier’ Works (1862) II 431: To strip the Isle of Rum of all its punch [...] Or doom – to suit your milk and water view – / The Isle of Skye to nothing but sky-blue!
1859, 1860		Hotten Dict. of Modern Sl. etc.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.

(b) (Aus./N.Z., also sky-bluer) a milkman or a nickname for a milkman.

1795		Sporting Mag. Sept. VI 315/2: Mr. Skyblue, the milkman.
1846		Bell’s Life in Sydney 29 Aug. 2/5: Sky-blue deposed that he was following his peaceful avocation in King- street, when Martin assailed him with scandalous vituperations.
1851		Bell’s Life in Sydney 12 Apr. 3/1: The well known Paddington sky-bluer, alias milk supplier to the metropolis.
1864		C.R. Thatcher Songs of the War 5: Milkmen give their customers warning / They’re leaving their usual walks / And off to the Wakamarina / Old Skyblue is walking his chalks [DNZE].
1908		Sun. Times (Perth) 14 June 1/1: Some of the skyblue fluid isn’t even second cousin to cow-juice.

(c) ‘London milk, much diluted with water, or from which the cream has been too closely skimmed’ (Hotten, 1860); ext. to weak milk in general.

1798		R. Bloomfield Farmer’s Boy n.p.: And strangers tell of three times skimmed sky-blue [F&H].
1828		G. Smeeton Doings in London 110: Thus milk is watered wholesale and retail [...] vulgarly called sky-blue.
1835		Comic Almanack Dec. 37: The Milkmaid, who deals out sky-blue.
1835		Sydney Herald 18 June 4/2: [A] dish of milk and water, riglar sky blue.
1841		Flash (NY) 3 Oct. n.p.: The milkman whooped [and] the vendor of ‘sky blue’ was lost [...] in admiration of the charm of the maid.
1843		R.S. Surtees Handley Cross (1854) 417: A small jug of ‘sky-blue,’ which the flies use as a bath durin’ their repast on the sugar.
1853		Bell’s Life in Sydney 5 Feb. 3/1: ‘Sky-blue,’ called by the uninitiated ‘milk’.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		Hills & Plains I 100: True, he used to be called General Green-grocer, and impudent young fellows used to shout at him, ‘How do, old sky- blue?’.
1864		G.A. Sala Quite Alone I 233: Cake and wine existed no more in her allure; she was suggestive only of bread and scrape and sky-blue.
1870		Hotten Sl. Dict.
1884		Ally Sloper’s Half Holiday 8 May 7/1: Where does London milk comes from? — Why, from Cowes, of course [...] I mean sky-blue skimmed.
1895		C. Crowe Aus. Sl. Dict. 75: Sky Blue, milk diluted with water.
1940		M. Marples Public School Slang 65: Milke [was] sky-blue because of its colour, due to a liberal admixture of water.

(d) vegetable soup.

1904		Number 1500 Life In Sing Sing 253: Sky blue. Vegetable soup.
1949		Monteleone Criminal Sl. (rev. edn).

(a) (Can.) an officer of the Hudson’s Bay Company, usu. in pl.

1984

Partridge DSUE (8th edn) 1081/2: since ca. 1815; by 1940, ob.

(b) (US) a soldier.

1851

M. Reid Scalp-Hunters II 5: He had been a soldier in a frontier post – one of uncle Sam’s ‘Sky-blues’.

(c) (S.Afr.) a long-term prisoner.

1946

Cape Times 23 May n.p.: If the ‘sky blue’, languishing in prison, considers that he has been framed by one of his previous cronies (variously known as chummies, pallie blues, or beans) he will ‘carry him in his heart’ until he can . . . get his revenge [DSUE].