We saw a guy on TV last night wearing a brown suit, and a comment was made that his suit was so "gumshoe."
It sounded right. The suit was dark brown and looked out of place, like he had just changed from his chaps. Clearly, he looked a bit like a cowboy in a suit.
Gumshoe is slang for detective.
So perhaps the guy on TV reminded us of the "Perry Mason" or "Ellery Queen" era. Or maybe "Dragnet."
Whatever the case, someone wearing a dark brown suit on TV will now inspire the comment, "that's so gumshoe."