Green’s Dictionary of Slang

of a woman, intellectual; thus (US campus) excessively hard-working, overly dedicated.

1825		J.K. Paulding John Bull in America 104: I one night, at a literary party, happened to mention some opinion from Lord Bacon to a young lady who had the reputation of being rather blue.
1842		Dickens Amer. Notes (1985) 50: Blue ladies there are, in Boston; but like philosophers of that colour and sex in most latitudes, they rather desire to be thought superior than to be so.
1843		Bellew Memoirs of a Griffin II 53: She was neither an envious old maid, nor a spiteful old maid, nor an intensely blue old maid, nor a canting old maid.
1852		F. Smedley Lewis Arundel 277: She had been growing decidedly blue. Not only had she, under Bray’s auspices, published a series of papers in Blunt’s Magazine, but she had positively written a child’s book.
1854		G.J. Whyte-Melville General Bounce (1891) 8: Though a pleasant, cheerful woman, she was decidedly blue – that is to say, besides being a good musician, linguist, draughtswoman, and worsted worker, she had a few ideas, not very correct, upon ancient history, a superficial knowledge of modern literature, thought Shakespeare vulgar and Milton dry, with a smattering of the ’ologies, and certain theories concerning chemistry, which, if reduced to practice, would have made her a most unsafe occupant for a ground-floor.
1865		G.A. Sala My Diary in America II 32: The Boston ladies are very literary; some of them are really very learned, and a few may be blue.