Recently, I decided to work a Fleegle heel in colorwork. Information on WS colorwork is most likely available on the web already. And there are probably much better ways to get the same result. But, here is my take (mostly for my own reference).
My main problem was seeing the stitch that I was going to purl into (possibly since I knit Continental style). For this colorwork, I had blue at the top, brown in the middle, and green for the bottom thread. Keeping an order like this helps keep the yarn from twisting. The picture shows preparation for purling in green with blue and brown off to the right side.
When preparing to knit in brown, I left green to the left and blue to the right. For blue, both green and brown were left to the left.
As a side note, when working on the RS, I kept the same order, with blue in my right hand, brown over the index finger on my left hand, and green over another finger on my left. This was my low tech way of keeping the yarn from twisting.
A final note (mostly to myself): After turning (for the short-row part of the heel), before making the first st in a row (after the slip stitch), wrap the other 2 yarns under the yarn to be used in that st. When I didn't do that, I had holes. For the pair of socks I made with this pattern, I left one heel with holes and one without to help me remember this.