The images you showed are of a Mercury-Atlas. The Atlas was made from very thin stainless steel sheet (the differences in texture you see are the "grain" in the metal from the individual sheets). It was unusual in that it was a "balloon tank" vehicle, e.g. there was no internal structure under the skin. The skin was the tank wall with only bulkheads to separate the propellants. It had to be kept pressurized when not fueled because it could not even support its own weight when empty (I have some video of an Atlas/Agena at Vandenberg folding up like cardboard during a fueling mishap).
Most rockets of the period were aluminum skin over a frame. Usually the skin was painted (Thor, Jupiter, etc.) but sometimes not (Titan).
You also have to decide what point in the flight you want to model. The Atlas, for example, looks all shiny when first set up on the pad, but after fueling and through launch, it's all white on the top two thirds from the frost around the LOX tank. You also, obviously, can't see the "UNITED STATES" running down the side under the frost. The Titans, conversely, use "room temperature" propellants (hydrazine and nitric acid) so even though they're unpainted, they look the same all the time.
- Jack
Jack Hagerty
ARA Press
www.arapress.com