[Espy]

If you want something that's monochrome, the shop items labeled "basic" are black, grays, and white. Some of them aren't labeled basic, though...and the white isn't as white as the "white" in silver items. Anyways, some items:

Threads:
Vest
Open Blouse

Eclectic Trends:
Collared Jacket
Street Tagger Blouse

Lavish Luxuries:
Blouse
Fancy Blouse
Business Tie
Business Pants
Business Vest
Argyle Sweater Vest
Business Jacket

Just search those item names and you'll see that item in all the available colors.

...Alternatively, you ca just search for a color (say, silver) and you'll get all the items in the shop that are silver. Which is...like...every item in the shop, once. Easy to see what the shop holds.