I started by knitting these according to the slipped stitch pattern in Geek Socks. However, the black stripes weren’t even and there were some dark grey or black flecks in the other colours.
Rather than just knit them in stocking stitch, I slipped alternate stitches in the first round of black (k1 sl1 k1 sl1) and the first round of the following colour (sl1 k1 sl1 k1) and this gave me little blocks of black like dotted lines.