Is it a sweater knit in one piece or are you making pieces that will be seamed together? How big is the stripe...I mean how many stitches? Either way you probably want to use intarsia rather than fair isle.
With fair isle you'd be carrying the color across the entire piece and only knit with it on the stripe.
With intarsia you have to have 3 skeins of yarn, one for each section. You don't carry the yarn you just twist the yarns at each edge so there isn't a gap/hole then knit with the next color.
There are instructions in the video section under advanced techniques.