The settings for this appear in their own section, called "Plugins by Crackpotx", instead of "Plugins", where I would expect them, but the main thing is: setting an overlay color does nothing. Unexplored areas are not colored with it, as you would expect.
I'm using this add-on with ElvUI 11.20

It is something with Blizzard's API. There does not appear to be anything I can do about it.