Hey Stormtrooper! Things are great, welcome to SPS!
Starting with GIMP isn't a bad choice. The color palette is easy to find, just double click the foreground or background colors in the main GIMP tool dialog, and you'll get a new window with a color palette. You can pick a variety of palette types on that dialog, just play with the radio buttons and tabs and see what all you can do.
I don't know anything about the Third Wire products, so I can't comment there. I would say that IL2 is a great place to start though, with straight forward techniques, easy .BMP file formatting, and ample starting materials.
Start by getting a feel of the work process, just drop by the tutorials section we've got here, and read some beginners guides like this or this. Then grab a layered template for a plane you'd like to skin in IL2 (we've got a handful in our downloads section), and start to play with things.
Finally, if you get stuck somewhere, it happens. Just post a question and we'll do our best to get you going.
Good luck... it can be an addictive hobby!![]()