I mostly wrote this just to see how locator() works, and ended up making an HCL color picker, so you can make your own visually offensive rainbow color palettes! Or, you can make your own nice color palettes. It is up to you.
Essentially, this script generates a fair number of color points in HCL space, allows you to click on them in any sequence you desire, and produces a color palette from your selections. Below is one of the infinite hideous possibilities:
I don’t have a lot of experience with locator(), but do be advised that its behavior seems to vary across GUIs/IDEs. For example, in RStudio you end the input session by typing [ESC], while in the standard Windows GUI, you seem to have to right-click and select Stop from the pop-up menu. Your mileage may vary.