Worked from the top down. Pattern is 72 stitches around (that is, two widths of a Hobbywool mitten design).
Technique for creating vertical lines (rather than diagonal) when doing tapestry crochet in the round found at http://alltapestrycrochet.com/creating-straight-vertical-... (Short version: sc blo with yarn under for the final pull-through). Also: remember that final pull-through needs to be in the next color when changing colors.
Note that individual stitches still read as diagonals, so the effect will be like slashes in ASCII art, not like Xs.
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If I were doing this again, I’d make the first row of the heel black, so that the color would meet up with the black band that comes after the heel.
Note that you really do need to have more stitches along the edge of the heel when resuming the rounds: the the foot won’t hang nicely at an angle if the circumference isn’t bigger than the rest of it for the first few rounds after the heel.