In the 1850s, American men started wearing ditto suits, or suits sewn with the exact same fabric for the suit jacket, the waistcoat, and the trousers.
This practice of choosing a waistcoat fabric that exactly matched the suit coat and trousers saved time and simplified the tailoring process.
As a result of the perceived ease in ordering a ditto suit (as waistcoats with suits were prominent in the 1800s and selecting a waistcoat fabric could be a thought-intensive process), the ditto became a less formal choice, and was generally worn for business, travel, or street wear (i).
Ditto Suit: The same fabric is used for the jacket, waistcoat and trousers. Above Cifonelli bespoke and Paul Stuart (Phineas Cole)
Before the ditto suit, most waistcoats did not match the suit jacket and trousers at all.
Compare the practice of using the same fabric for the entire suit as shown above, with the practice of choosing a fabric for the waistcoat that contrasts the suit fabric. Here we see some nice examples :
Above : Ralph Lauren, The Armoury / Ring Jacket and an interesting twist by Mararo, with a mismatched jacket.
While the general rule for selecting a contrasting waistcoat is to choose a fabric with obvious color and design variation, your eye will be the ultimate decision-maker on what looks good, and what does not.
One of the benefits to contrasting the waistcoat with the base suit fabric is that the same waistcoat can be used with multiple suits, yielding more suit ensembles…a plus when overall cost and closet space are important factors in building your wardrobe.
I. Bigelow, Marybelle S. Fashion in History: Western Dress, Prehistoric to Present. Minneapolis, MN: Burgess Publishing 1970.