Recoloring Tips Wanted!

So, as some of you know, I've been wanting to learn how to recolor. I love airliners, and there are so many I would like to do. However, I always get lost when I open up Inkscape. I can make shapes, manipulate objects, draw lines, etc. However, I just don't know where to start! Do I take a logo and trace it, do I freehand it, do I take a decals sheet, trace the bitmap, and paste it on to the template? I don't know. I also don't know what to do with placing logos and symbols on the template. I never can find any resources on the livery dimensions/specifications. Where do you guys find the right color to use for a livery? If you can chip in with any tips, it would be much appreciated. I have 5 hours in a plane to burn on Wednesday, and I really want to learn how to properly recolor. Thanks!