33 upper door frame sill plates

[Doctor's Ford]

I will shortly install these sill plates removed from my car near 4 years ago and need to answer a few questions. They are on primer now. What exactly are they for? Are they painted body color or do they have the same finish than door/window garnish molding? Are they visible or will be covered by the upholstery? My car is a 33 Tudor Deluxe. Thanks for any input you can provide. Manuel