The exact origin of this theatrical name for the room in which actors wait for their cues is not known. It probably refers to a room that was actually painted green, but which room and which theater is lost to the ages. The earliest uses are in reference to the London theater. From Colley Cibber’s 1701 Love Makes A Man:
I do know London pretty well, and the Side-box, Sir, and behind the Scenes; ay, and the Green-Room, and all the Girls and Women~Actresses there.
There is lots of theatrical folklore associated with the name, none of it with any basis in fact. Often it is stated that the room is green because this is a soothing color—which is probably not true as this relies on 20th century psychological theory. Another story is that it is called green because the actors would also be paid here—but English money isn’t green like U.S. currency. Besides, in 1701 they would most likely be paid in coin, not notes.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton