ERRATUM - Row 40 should be to last 14 stitches, not last 13.
This is much, much easier than it looks.
Only 1 row in 8 requires a tiny bit of concentration (and there are tips to help with that).
Use a nice soft yarn up around your neck and then for the colourwork use something fancy - you’ll only need about 120-150m (135-180yds) :
maybe even variegated.
Many thanks to the testers for their feedback and beautiful knits: