See that line of pink stitches with pink wool dangling from it? When I have finished knitting the toes of the sock, I will come back to those pink stitches and remove them. That will leave loops on either side of the row, which I will pick up with double pointed needles. Then I will knit an 'afterthought' heel.
The stitch I have used here is called Little Arrows, from a pattern by Susan Brugger, though I have adapted it to my own sock pattern. I like the way the textured pattern muddles up the colours of the wool. On the plain part at the bottom of the foot, the colours appear as much more obvious stripes