The yarn is Cascade 220 Heathers in #4011, a grey with a very slight greenish cast. The shade has a lot of depth, but it's not coming across very well in these photos. The horseshoe cable surrounded by seed stitch is the same one I used in the Murray Jacket (still to be written up).
I chose to bring the cable around the ankle, with the decreases on top of the foot and the ribs coming together on the instep, like this.
What a great go-together with the BT hat I finished up yesterday!
I need to run out now and purchase a second skein to finish the pair.