This is the best example for study that I have. I think it was done by waffle or octavius; can't recall now. It's the profile of a
P-47D-25:
You can export your own D25 skin, cut this jpg out and paste it into the D25 bmp and make your own custom skin to see how fantastic it looks in game.
Use photoshop's color wand to get exact values for the different colors of grey/silver in the jpg. Try to duplicate it, start with the lighter colors first and airbrush in the darker layers, working up gradually. Use fairly contrasting colors, too - if the grey shades are too close, it gives a bland, milky appearance - look at my in game P-47D11 skin's wings from the cockpit and you'll see what I mean. I dont' think I used enough contrast in the shades there.
Another trick to use is to color in a few random panel sections darker or lighter than the base aluminum color you use.
Also study the natural aluminum profiles in Osprey's P-47 and P-51 "Aces" books.
Keep experimenting and good luck!