talks about it a bit (towards the middle of the page). What I think you do (and what I've done) is just knit with one color, drop that yarn and knit with the new color, and then as long as you have an even number of rows in your stripes, you'll end up on the side where you left the first yarn. Just pick that up and start using it again! You just have to make sure that you don't pull too tight or let it hang loosely when you start using it again. And the site recommends not carrying it more than 1/2"