Rod,
On a scheme like on the race car in the pic, all you really only need to concentrate on would be the red area. Everything behind this will be blue. Everything in front of it will be the yellow.
There are several ways to do this, but one way would be to mask up the side of the car using 'automask' (or even two inch tape). Then you would draw out with a pencil where you want the graphic to be. Then cut this area out. Then mask up the other side. Then you use the part that you cut out on the one side reverse it, tape it on top of the mask on the other side, then draw around the edges of the cut mask. Then of course, you would cut this out.
Keep in mind, you only have to mask up where you plan on drawing the red stripe.
Of course, you will have to use paper to cover the rest of the car when you spray the red.
Doing it this way lets you draw some pretty radical jagged edges.
Then you could have a stripper come out and handstripe the edges.
OR
If you only want a 'few' jagged edges on the red stripe, you could just use 1/8" fineline and hand layout the stripe. Then you would have to take measurements to use for the other side. This will get side to side close.
There are also several different ways you could do this. You could even do the red first, then mask UP the red area instead of masking AROUND it. Then you would do the blue behind the stripe and the yellow in front of the stripe.
Just some ideas for you!