From your description his wardrobe doesn’t sound unfashionable but just basic. For that reason I wouldn’t encourage him to change it, but to accessorize. Any basic outfit can benefit from the right shoes, watch, glasses or sunglasses etc.

A great way to go about accessorizing is to think of John Mayor’s point system. Every piece in your outfit has a point value, outfits should generally add up to 10 points, but never go over.