This is Midnight Rainbow Brite self-striping yarn by Mothy and the Squid. I bought the yarn at Yarningham and knew it wouldn't be long before I used it. My kids have been begging me to make rainbow socks for them too. I used 72g for these, from a 100g skein, so I'll have to combine it with something else to get enough yardage for a pair of kid-sized socks too. Or maybe I'll just have to buy another skein.
The colours are amazing, the yarn is lovely to work with, and it held up well to being frogged as well (I'd made the heel flap too short on the left foot so it was too tight on the instep and I ended up ripping back and re-knitting the foot down to the toe).
I strongly suspect there will be more rainbow-striped socks in my future pretty soon.