Variegated yarns can be great because they make a design in the fabric just by doing a basic stitch.
Then the pattern gets interrupted, sometimes by shaping in the construction, but also sometimes by breaks in the yarn, when there are knots. Then the piece can come out looking goofy.
One solution is to control the color changes, breaking the yarn as needed to place the colors where I want them. I am not going to do that for two reasons: first, it involves too much micromanaging of the yarn, and second, it ends up wasting a bunch of yarn. So what else could I do?
I turned the project on its side, starting at the side seam, working back and forth with all the shaping on one edge, and the other edge (the bottom edge of the vest) with no shaping at all.
Suddenly, the colorwork turned into something like ikat, with lots of vertical lines. The disruptions caused by the shaping became irrelevant. And the vest turned out just fine.