Interesting. After digging in the source code a bit, I had come up with this as an experiment:
'#LineReaderClass.COMPLETION_STYLE_LIST_BACKGROUND#' : 'bg:blue',
'#LineReaderClass.COMPLETION_STYLE_LIST_DESCRIPTION#' : 'fg:~grey'
Should I be using the syntax you showed, or is what I have above also acceptable? it also seems a little redundant to need to specify "bg" for a setting that already has the word "background" in the name. Is this really correct?
That said, it also seems the commit yesterday did more than just change the names of the variables and the format they expect. The menu list no longer behaves the same color-wise as it did in the previous snapshot build. Now my background color isn't being applied to the description and the highlight color is different now as well (back to pink).
It would be nice to get a little better documentation and/or direction on what's changed between the code 2 days ago and the code today and how I'm expected to get the same behavior back that I had in Jline's 3.17 snapshots. After all the testing this last week, I was hoping to make a release today, but this last minute change committed yesterday prior to the stable release has thrown a wrench in the gears.