My father is a retired painter. He worked for 35+ years painting everything from water towers to special high end work interior paint jobs.
the one thing that i did learn from him was to always apply the lighter colored paint first. if you paint on the darker color it will take multiple coats of the lighter to cover it.
I did my mini-bertha all black with one whole fin white. i first painted the white fin - waited 2 whole days (darn hard to do)
then i wrapped the fin with a piece of a grocery bag and applied painters tape along body tube/fillet edge to hold the paper in place.
i applied a thin coat of black paint, waited about 10 minutes and then applied another thin coat and waited only a couple of minutes and removed the tape and paper. by removing the tape and paper when the paint is wet the edge of the paint will just flow over the edge of the paint line - not run- and seal the edge so that it is really smooth. it also helps to keep the paint from peeling away with the tape.
i follow a similar technique when i paint a band around a body tube.
removing the tape when the paint is still wet is something that a some of the old airplane painters will do. they do it because if there was a rough edge to the paint then the wind going over the wing would slowly pull the paint right off.