In the fashion industry, ribbing with a contrasting color at its edge is referred to as "tipped". I like to incorporate tipped edges into my designs as a way of outlining or underscoring each piece. And because I think single-color ribbed edges are boring. Here's the tipped edge I made for my "Waves" cardi:
It's actually a rolled bit of stockinette stitch, adjacent to the 2 x 2 ribbing.
And here is the (nearly - still needs buttons) complete Fugl, with spring green tipped edges. I love the way it looks, and it's really fun to knit, with one tiny issue: Knitting doesn't work that way. In my hands, at least, knitting works like this:
First I knit the neckline ribbing, with a swell green bind off edge. Then I work a placket, at 90 degrees to that, with its own green bind off. Which leaves a gap with NO green bind off, at the top and the bottom of the button placket. This bugs me. And here "bugs" may mean night terrors, brain fissures, and/or feelings of inadequacy.
Steps must be taken.
Unable to leave such affronts unchallenged, I handle it like this:
First, with the tipping color, I pick up and knit through the "naked" edge, the number of stitches I think look pretty. In this case, it was seven.
Then I execute whichever honorable and impressive bind-off maneuver I used for the rest of the edges. After that, I use the yarn tails to darn the "filler" edging to the previously-worked ones, if necessary, and Voila! Self-satisfied smugness is achieved. Fiddly? a bit. But preferable to brain fissures.
If you elect to try out your own tipped edges, remember to work the first row of your color change in all KNIT stitches. That way you'll avoid forming yucky bi-color purl bumps. For example, the sewn tubular bind off above is a two-row gig, so first I work a row of all knits in the new color, then proceed with my two-row bind off pattern. Capiche?
Try a tipped edge (either cast on or bind off) next time you need to make a swatch. Look how smart you are!