Make a chain stripe in your knitting - this tutorial was made to show the embellishment option for the arctic habitat of the Adventure Knitting 3 collection, but it can be done on any knit fabric with stripes of eyelet holes, or on a loose-gauge knit fabric (so the fabric is open enough to stick the crochet hook right through the stitches).

(or see the video on YouTube here)

pull contrasting color yarn through eyelet hole, from the front/right side, sticking hook through to back/wrong side, pulling yarn loop to front (tail and working yarn hanging out back)

with yarn loop on hook, stick hook through the next eyelet hole up and grab contrasting yarn, pulling it through that hole, then continue pulling new loop, through first loop

repeat the last step, pulling yarn through next hole up, then through loop, up the stripe of eyelet holes for as long as you want your stripe

when you're finished, break contrasting yarn in back, then work the step normally, but continue pulling it once it's through the previous loop, all the way through

pull tail through eyelet hole to back side, and weave in ends