Paint the walls shades of cream, light blue, light green or pastel yellow. Only extremely wealthy colonists could afford wallpaper in the 18th century, so pick just one room for wallpaper, in keeping with the frugal quality of the Cape home. If you do opt for wallpaper select an understated floral pattern in keeping with the era.
Expose all wooden beams, if they're not already exposed. Keep the wood floors bare, except for a modest braided rug here and there.
Furnish your home with Colonial- or Federal-style wood pieces, in keeping with the modest theme of the home. You can splurge on some very plush upholstered armchairs or a couch, but they should reflect the color palette of the Colonial era: blues, greens, creams and browns, with a red accent here and there.
Install wall scones that look like kerosene lanterns. This will give your home the antiquated charm of such light fixtures, with the convenience of electricity.
Outfit each room with humble decorative accessories. For example, in the dining room, a simple hutch displaying your china works well as a modest decoration. In the living room, a bookshelf with leather-bound books or a figurine or antique clock will suffice.