“He had drifted across the passage into his bedroom, and was changing with a rapidity one might not have expected from a man of his mannerisms. He selected a dark green tie to match his socks and tied it accurately without hesitation or the slightest compression of his lips; substituted a pair of brown shoes for his black ones, slipped a monocle into his breast pocket, and took up a beautiful Malacca walking stick with a heavy silver knob.”
Sayers, Dorothy. Whose Body? 1923. Reprint, New York: Dover, 2009.
The shift from black to brown walking shoes signifies a shift to a lesser formality. As previously remarked, Peter doesn’t think dressing formally would be enough to rattle Mr. Thipps – instead, he wants to dress familiarly and comfortingly, so as to make Thipps confide in him. Changing into a grey suit and brown shoes, as opposed to frock and black shoes, brings his clothing into Thipps’s social register.