I have set up a fresh install for a new site, and decided to trial the implementation of the Theme Colors filter to set up some unchangeable colors.
However, when there are many Theme Colors set up but no Palette Colors, the color picker shows only the HSL picker and no list of colors. As soon as I add any auto generated color to the Palette, all of the Theme Colors show up.
Adding an auto generated color
This initially occurred on a custom stack that extended the Starter stack, but also occurs on all other stacks to after testing.