There are differing alloys on aircraft depending upon the area. These vary in color. Hot spots will use steel, others are heat treated differently for stiffness, etc. If accuracy is desired it would serve the modeler to do a little homework on each model where natural metal is the ultimate finish.
Weathered natural metal aircraft really don't look silver anymore. They are really what I'd call gray with highlights of aluminum, titanium and steel suggested in a method that Rub-N-Buff might pull off well. The model might be painted with low-lights over sub-skin structural members, finished in a very light (completely flat) gray and then, using a soft cloth dampened with a metallic color (like dry brush) it can be lightly buffed onto the skins bordered by the underlying structure and feathered out into the gray. These would be the panels themselves. Brand new factory roll-outs will look bright indeed but I've yet to see a model give that appearance in scale. This model of a Republic RF-84F Thunderflash was painted in flat aluminum overall. Structural detail was "picked out" using a regular number 2 pencil and an artist's felt blending stump.
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