Source: Nancy Marchant’s Knitting Fresh Brioche: Creating Two-Color Twists & Turns, p. 128.

MIGHT BE USEFUL: since I’m extremely bad at purling, I reversed the direction of knitting after every sub-row & thus knit the other sub-row (of a pair) instead of purling it. There is another benefit of such an approach: you face alternatively either side of the knitting and have a chance of spotting possible mistakes (slipped yarn-overs) much sooner than with the traditional method.