I think I can safely say that the interior color of the decklid was always body color. Speaking for the cars in that era, the trunk had cardboard panels inserted with a fabric cemented to them. The deck interior of my 38-60S is still original and the trunk floor has a ribbed rbber mat, cut to fit the floor. Since its a 6 wheel model, the entire trunk floor has the mat.
In some instances, and Im referring to the 90 series cars, both my 38 and 39 90 cars had wood framed decklids, and had a carpeting on the decklid interior, and the carpeting had binding on its periphery. The rest of the trunk was done similarly.
Indeed, they didnt spiff it up as much on the LaSalles!