The highlighted text refers back to a line in the very first paragraph of the containing chapter...
His coat is a colour, and cut, that never was the mode anywhere, at any period.
I assume the reference to "colour" is self-explanatory. The "cut" of an item of clothing refers to how the different pieces of cloth making up a garment are shaped and stitched together so as to fit the body well (or hang down elegantly, as appropriate). And never was the mode is just a slightly "literary" alternative to was never fashionable / in fashion.
So the text is saying the coat was very "unusual" - probably not in a good way, but the OP here can decide for himself whether it's an unusually good or unusually bad looking coat.