To sum up the technique before I show you, basically you tape off the outside of the line, then paint along the inside (where the line color will go) with the base color of the wall and let it dry. That way you're creating a seal along the tape line, and anything that will have dripped behind it will be the same color as the wall. Then you'll paint the line color. Since this is a bit confusing, I took pictures along the way...
By far the hardest part of this process was taping off the initial line for me. I used a level at first and went around the entire room. When I got back to where I began and took a step back, the line was 2 inches from the ceiling in some places and 4 inches in others. Clearly our ceilings are very imperfect. I erased everything and started over using a different method. I measured 3 inches down from the ceiling all around the room in various places. Then I used my rotary cutting ruler which is 6 inches wide to draw the lines. I lined up the top with the line at 3", then drew my lines along the top and bottom of the ruler giving me 2 perfectly parallel lines 6 inches apart. When I was pleased with how that looked, I added the tape right along the line.Next I painted the inside of that taped section with the wall color to seal the tape and let it dry.The widest stripe in the room is chocolate brown. When the base coat of wall color was dry, I painted the entire stripe chocolate brown. When it was dry, I removed the tape and was shocked at how little it ran. After all that work I was thrilled with how little touch-up I'd have to do.It's important to mention that you really need to wait until the paint is completely dry before beginning the next color. I let mine dry overnight. Next was the red stripe. I wanted it to be one inch inside the chocolate brown stripe, so I lined up one inch wide painter's tape just along the chocolate stripe edge. For example, the top piece of tape pictured is lined up with the top edge of the chocolate line.The next step is to paint just inside the tape with the chocolate brown paint since this is now the base color.When this was dry, I painted the red.Then I removed the tape revealing a one inch chocolate border on either side of the red.To finish, I repeated the taping for the navy stripe. I wanted the navy to be a much thinner line, so I used 1 1/2 inch painter's tape along the edge of the red line. This way the navy stripe was one inch wide. So I taped, painted the red in between, let it dry, then painted the navy blue stripe. The result is the picture at the top.
What little touch-up necessary was done with just a small artist's brush. I couldn't be happier with how it turned out, although I'll admit it was a process that required a LOT of patience. But I'm the type of person that prefers to do the work along the way than to have to clean up my mess when I'm done. This technique is perfect for that tendency.
Anyone have any more helpful hints or tips?