How it's actually done is as follows. It would work the same if you're using brushes to paint the lines. Here i'll show how i made the black stripes on my fire prism.
2. Sprayed black on the areas where i wanted it to be black.
3. Using a 1cm wide ordinary masking tape, i masked the area where i want the black stripe to be. Weaken the tape's adhesive by sticking it to paper or slighty dusty surface before applying to the surface.
I usually allow the paint to dry 24 hrs before applying the masking tape but if time is of essence, then i use a hair dryer.
7. Carefully peel off the masking tape. Peel the tape at a 90 degree angle to prevent the tape from peeling the paint off. Some paint might/will be peeled off but this can be repaired using brushes.
9. Carefully paint outlines using blazing orange along the red areas. And that's it.
10. Coated using semi-gloss varnish. Blood red would change to a dark hue.
11. Final product. I know its a big leap from Step 10 but just wanted to show how it looked like when finished.
Hope this helps. I have done some commission work for friends in the past. Wouldn't mind doing it again just to help you get your models painted ASAP. But only for spraying base coats, primary colors or stripes/simple designs. Minimal fee. Neatness guaranteed. Hehehehe.