A public-house sign; the cognisance of Richard III. In Leicester is a lane in the parish of St. Nicholas, called the Blue Boar Lane, because Richard slept there the night before the battle of Bosworth Field.
The bristly boar, in infant gore, Wallows beneath the thorny shade.
Gray: The Bard.
England shall many a day Tell of the bloody fray, When the blue bonnets came over the border.
Short Acts of Parliament, etc., even without a wrapper, come under the same designation. In America, the “Blue Books” (like our “Red Books”) contain lists of those persons who hold government appointments. The official colour of Spain is red, of Italy green, of France yellow, of Germany and Portugal white.
“You proud varlets, you need not be ashamed to wear blue, when your master is one of your fellows.” —Dekker: The Honest Whore (1602).
“I'll have you soundly swinged for this, you blue-bottle rogue.”—Shakespeare: 2 Hen. IV., act v. 4.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894