Entry in progress—B.P.
 
Broolyn Newsstand
3 July 1887, Brooklyn (NY) Daily Eagle, “Restaurant Calls,” pg. 13, col. 1:
“Coffee in the dark” and “slops in the cup with the light out” signify coffee without milk.
 
Chronicling America
1 March 1888, Mexico (MO) Weekly Ledger, pg. 4, col. 4:
Coffee in the Dark.
From the New York Sun.
In the Bowery eating-houses haunted by newsboys many acticles of diet have more picturesque designations than elsewhere, Such, for example, as
 
Hash—The mystery.
Bread—The necessary.
Coffee minus milk—Coffee in the dark.
 
Hudson River Valley Heritage Historical Newspapers (NY)
24 March 1888, The Rockland County Journal (NY), “Waiters’ Queer Orders,” pg. 6, col. 1: 
A NEWS reporter went into a restaurant on Ann street yesterday and after having given his order to the waiter asked him what was the meaning of the jargon waiters usually shriek at the cook.
(...)
If you give an order for a cup of black coffee you will hear the waiter call forth, “One in the dark.”
(...)
—N. Y. News.
 
Brooklyn Newsstand
15 November 1902, Brooklyn (NY) Daily Eagle, “The Buckwheat of To-day,” pg. 12, col. 4:
This means that the buckwheat season has come around again, and that guests who have for months been ordering “one on,” “coffee in the dark,” “white wings, sunny side up,” “one dyspepsia in a snowstorm,” “beef an’,” “brass band without a leader,” “one wheat an’ one sweet,” “make it punkin,” “mystery without onions” and “plate o’ wheat” are varying the round of etymological gayeties by commanding the waiter to “brown the bucks.”