Well..........
I don't have a "plan", usually.
I often build *replicas* of Classic planes so I just use the original colors and scheme for them.
On my modern planes I might steal a scheme from someone else, or just *start* on the finish and see what comes out!
Contrary to Steve, I almost *NEVER* have the paint scheme in mind before I start painting.

My next PAMPA plane scheme is already figured out simply because it is a semi (way *semi*) scale plane.