It sounds like you're changing colors at the end of the row, so you can carry the color not in use up the side edge. They are probably asking for the inside edge so that the carried yarn is in or near the seam.
You can catch the carried color with the working yarn if you want to minimize the look of a loose loop at the edge, if you want. Just remember to carry it fairly loosely so it doesn't pull at the edge sts. I assume the yarn is only being carried for a few rows since the pattern is telling you to do so.