I've decided on a different stitch pattern and now I'm much happier with the vest project!
I'm stranding two balls of the same "W-EC" colourway of Kauni against one another, just starting each ball in a different section of the colour sequence. I'm using Knitpicks Palette yarn in "Heathered Garnet" as the fleck of contrast. If you look closely at the picture (clicking on it will enlarge it a bit) you can see how the patterning is gradually getting darker. That is not just a trick of the light. The background and foreground are both getting darker in this section.
There are mistakes. I'll use duplicate stitch to camouflage them when I am done.