I'm thinking of something that would be worn under the five button waistcoat, but outside of the shirt. Somewhat like a four-in-hand tie, but more frilly.

Although, my question now is what kind of neck wear was being worn in a lot of the eighteenth century depictions of the American colonials and Founding Father's? Just from memory, it seems like the same kind of jabot, and cravat looking type neck wear.