They have you work back and forth on the 3 needles to keep the edges from getting all stretched out, as well as to work the color pattern. You can just work back and forth (knit rs, purl ws) until you've worked the length of the color pattern--this will leave the thumb as written.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry