I painted a triple stripe in my son's room. First with blue painter's tape, then moved to frog (green) tape.
Blue sucks and is there to stop drips/overages. I had to wipe up quickly.
The frog tape actually stopped the paint (barring corners) and made for nice lines.
If you are trying to do lines, you will have to do this for blue tape.
1. Put tape up and paint over the tape seam with the base color. If you have to paint the base color first, do that.
2. Paint the top color over the base color and allow to dry. Once dry, remove tape carefully and should have clean lines.
example: I have cra**y builder beige paint. So I painted the walls blue, let it dry. Then I taped up the brown portion of the stripe on the wall, painted the tape with the same blue. Allowed it to dry, then painted the brown. After the brown was painted, pulled the tape off and had a nice clean line.
~egon