Masking stripes or designs can be done much better if
plastic "Fine Line" tape is used.
This tape is used along the edge where the color will change then the rest of the panel is masked using standard masking tape and paper.
The Fine Line tape will stop bleeding along the edge and the
result will be a nice clean break between colors if
the tape is applied properly.
When removing this plastic tape you should pull it back on itself as a sharp angle so that it cuts the paint cleanly.
Fine Line Tape can be found HERE.