The term a brown study was used in a book I was reading a couple of days ago. It seemed like a new phrase to me - or perhaps I had read it before and was able to construe its meaning, therefore not bothering to look it up.
The term dates from the sixteenth century and while used in novels by authors such as Dickens, Doyle and Alcott, it eventually fell out of the popular vernacular.
I've always favored the color brown. All my life I have been contemplative. One of my high school senior picture poses could have been a brown study without me even being aware.