When I wanted to dye some self striping yarn for my Jaywalkers, I started by knitting a few rows in the necessary guage. Then I frogged it and measured the yarn I had used and divided by the rows I had knitted. That way I knew how much yarn was needed for one row. Then I made it into a huge loop and divided it into sections for that yardage and dyed each section a different color. Thankfully, it worked out perfectly. I imagine this is generally how manufacturers do self-striping yarn. They probably just use the average guage for a pair of socks, and make the stripes like that. And like someone else had mentioned, even if it changes in the middle of a row, you're not going to notice on a pair of socks. Maybe that was not the information you were wanting, but I just thought I'd explain how I did mine. Hopefully it helped.