I agree that the two or three piece method is the only way to go. Here's the way I get perfectly straight lines along a wing leading/trailing edge for a two color scheme. I cover the wing with different colors top and bottom. I get the leading/trailing edges "close", but perfect is impossible if the wing is multi-tapered or elliptical. After covering, I cut a 1/4" strip of either color from the material. You can use several pieces if it's not practical to cut a piece the length of each wing panel. Using masking tape to hold everything straight, I low heat the strip over the seam and the result is a perfectly straight edge the full length of the wing. I use the same method along tail to fuselage attach points and to clean up edges of color trim on the fuselage. I think this will work for your project.

Good luck,
Paul