As No.1 says, you've got the right idea on the colors
. One of the challenges of shiny bare metal is getting that sense of reflectivity in. You've got the nice, deep blue reflection on the upper surfaces that you would see at altitude. The hard part will be to choose the other tones that you use. Depending on whether the aircraft is flying above clouds or terrain, the bottom surfaces can reflect the bright light of the cloud layer or the dark ground, which does not reflect much light. The light reflected from a cloud layer can remove most of the shadows on the bottom of the plane, causing you problems when you try to achieve a 3D effect. The good part is that you're doing it on the computer, so you get to try it over and over until you're satisfied
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Layers, layers, layers, that's one thing I've learned in my limited exposure to digital art. I'm afraid that I'm pretty much a traditional artist, not a digital artist like No.1, so other than making use of layers, I do everything with the brush/airbrush/pencil and eraser with occasional forays into masks and solid fills. At least I don't have to clean up the mess that I always make with paints
. I think that you're in good hands with his tutorial.