bluestocking n.

"of the color of the clear sky," c. 1300, bleu, blwe, etc., "sky-colored," also "livid, lead-colored," from Old French blo, bleu "pale, pallid, wan, light-colored; blond; discolored; blue, blue-gray," from Frankish *blao or some other Germanic source, from Proto-Germanic *blæwaz (source also of Old English blaw, Old Saxon and Old High German blao, Danish blaa, Swedish blå, Old Frisian blau, Middle Dutch bla, Dutch blauw, German blau "blue").

This is from PIE *bhle-was "light-colored, blue, blond, yellow," from root *bhel- (1) "to shine, flash, burn," also "shining white" and forming words for bright colors. The same PIE root yielded Latin flavus "yellow," Old Spanish blavo "yellowish-gray," Greek phalos "white," Welsh blawr "gray," showing the slipperiness of definition in Indo-European color-words. Many Indo-European languages seem to have had a word to describe the color of the sea, encompassing blue and green and gray; such as Irish glass (from PIE root *ghel- (2) "to shine,"); Old English hæwen "blue, gray," related to har (see hoar); Serbo-Croatian sinji "gray-blue, sea-green;" Lithuanian šyvas, Russian sivyj "gray."

The exact color to which the Gmc. term applies varies in the older dialects; M.H.G. bla is also 'yellow,' whereas the Scandinavian words may refer esp. to a deep, swarthy black, e.g. O.N. blamaðr, N.Icel. blamaður 'Negro' [Buck] 

The present spelling in English is since 16c., common from c. 1700. The sense "lead-colored, blackish-blue, darkened as if by bruising" is perhaps by way of the Old Norse cognate bla "livid, lead-colored." It is the meaning in black and blue, and blue in the face "livid with effort" (1864, earlier black and blue in the face, 1829).

The color of constancy since Chaucer at least, but apparently for no deeper reason than the rhyme in true blue (c. 1500). The figurative meaning "sad, sorrowful, afflicted with low spirits" is from c. 1400, perhaps from the "livid" sense and implying a bruised heart or feelings. Of women, "learned, pedantic," by 1788 (see bluestocking). In some phrases, such as blue murder, it appears to be merely intensive.

Few words enter more largely into the composition of slang, and colloquialisms bordering on slang, than does the word BLUE. Expressive alike of the utmost contempt, as of all that men hold dearest and love best, its manifold combinations, in ever varying shades of meaning, greet the philologist at every turn. [John S. Farmer, "Slang and Its Analogues Past and Present," 1890, p.252] 

Blue pencil as an editor's characteristic tool to mark corrections in copy is from 1885; also as a verb from 1885. The fabulous story of Blue-beard, who kept his murdered wives in a locked room, is in English from 1798. For blue ribbon see cordon bleu under cordon. Blue whale is attested from 1851, so called for its color. Blue cheese is from 1862. Blue water "the open ocean" is from 1822. Blue streak, of something resembling a bolt of lightning (for quickness, intensity, etc.) is from 1830, Kentucky slang. Delaware has been the Blue Hen State at least since 1830, supposedly from a nickname of its regiments in the Revolutionary War.

"close-fitting garment covering the foot and lower leg," 1580s, from stock "leg covering, stocking" (late 15c.), from Old English stocu "sleeve," related to Old English stocc "trunk, log" (see stock (n.1)). Probably so called because of a fancied resemblance of legs to tree trunks, or a reference to the punishing stocks. Cognates include Old Norse stuka, Old High German stuhha, from the same Proto-Germanic source. Restriction to women's hose is 20c. As a receptacle for Christmas presents, attested from 1853; hence stocking stuffer first recorded 1945. Stocking-feet "without shoes" is from 1802.

severe Puritanical code said to have been enacted mid-17c. at the founding of New Haven and Connecticut colonies, 1781; of uncertain signification, perhaps from the notion of coldness, or from one of the figurative senses in blue (adj.1). Blue was the color adopted by 17c. Scottish Covenanters (in contradistinction to the royal red) and hence the color for a time acquired an association with strictness in morals or religion. Or perhaps connected to bluestocking in the sense of "puritanically plain or mean" (see bluestocking, which is a different application of the same term); the parliament of 1653 was derisively called the bluestocking parliament.

The assertion by some writers of the existence of the blue laws has no other basis than the adoption by the first authorities of the New Haven colony of the Scriptures as their code of law and government, and their strict application of Mosaic principles. [Century Dictionary]

Long, detailed lists of them often are given, but the original reference (in an anonymous history of Connecticut printed in London during the Revolution) says they were so-called by the neighboring colonies, "were never suffered to be printed," and then gives its own long list of them in quotations. The common explanation (dating to 1788) that they were written on blue paper is not now considered valid.