Well, this is how I do it in photoshop. Apologies for replicating what I also just posted in the Custom Skins thread, but until I can find a video program that will screen capture for me, this is probably the best I can do. The terms and such I've used are for Photoshop, hope they help you.
What you do is this:
Use "unGTP.exe" - available at www.RoF-tools.de
to uncompress the GTP archives that Neoqb have bundled up game assets in to. Do this by downloading and unpacking unGTP, and placing it in your Rise of Flight directory. Drag the GTP file you want to extract onto unGTP.exe, it'll unpack it into a directory named (null). I forget which GTP file most of the aircraft skins are in - just unpack 'em all then look for the /null/data/graphics/skins/ folder. You can delete all the others.
Aircraft skins are in a folder named after the aircraft. They're stored in .dds format, which is a compressed texture format often used by games. You'll need the DDS tool from nVidia for Photoshop (or a similar tool for Paint Shop Pro) to be able to load and create them.
Load one of the basic DDS files into Photoshop, you get a 2048x4095 pixel image. The first 2048x2048 pixels are the main skin - what's seen up close. The next bit is 1024x1024, which is seen slightly when you're a little further away, then it's 512x512, 256x256 etc etc. Each of these different areas of the image are loaded as the camera moves away from the aircraft (saves on resources).
What needs to be understood is that this skin is a 2D image of a 3D object. So, it's like a peeled orange skin - it makes a 3D form when folded back up together. All the parts of the plane are there... just not where you'd maybe expect to find them. The wheels could be placed next to the tail, for example. The game itself knows where everything is, and will piece it all back together properly.
You can now edit this skin as you wish. The best way to do this, if you want to change the colour of the aircraft, for example (rather than just add icons/logos/text over the top of the current skin) - is to do the following:
Promote the locked background image to a new layer. Call it "Base" or something similar.
On the base layer, use the selection tools to only select an area you want to change the colour of. For example, the top/left/right sides of the fuselage. Get the selection to be a nice, snug fit around the aircraft body.
Then, with this selection still active, create a new layer. Call this one "Fuselage" (or whatever part of the plane you've got selected). Now, fill the selected area with pure white.
Go to the blending options for the new layer, and make pure white invisible by adjusting the blending slider. You can now use the "Colour Overlay" options to quickly and easily experiment with a fill mode and colour hue that will adjust the underlying base layer to the new colour you want. I find for light areas, using: DARKEN with about 60% opacity on the colour fill works well. For dark areas, LIGHTEN with about 30% works well.
This is MUCH harder if there is a lot of detail underneath the colour overlay. Ideally you want the base skin to be as simple and plain as possible. Most of the aircraft have at least one skin that's not got much on it.
It's important to leave some of the detail on the original skin showing through, otherwise you end up with a plastic-looking skin. By simply lightening or darkening the current skin with a new colour, you get a pretty good effect.