Are there just two colors? If so...work a stripe (color A) as far as you'd like, carrying the 'resting yarn' (B) up between the 2 & 3 stitch from the edge.
(not at the edge...it gets messy on the edge of a scarf)
Each time you go down and back and reach the resting yarn B, let the working yarn A 'tag it in' (a wrap) to secure it in the new row, but continue on with A for as many add'l rows as you like. But make sure A keeps tagging in B, to keep B secured in the newest row.
When you are finally satisfied with the width/height of the working yarn color A, at the place where the resting yarn B has been waiting her turn, drop A and pick up B.
It would be impossibly confusing to carry more than two colors this way.
However, you can alternate as many color stripes as you like, but just two at a time for the "carrying up' partnership. Example: A & B work together; C & D work together; E & F work together.