This is my first attempt at a Joplin plugin.
The plugin allows the user to auto insert the
MARK or a
SPAN tag containing a number of pre-selected background text colours.
The JPL package is downloadable from Github - JoplinDave/joplin-plugin-highlighter: Highlighter plugin for the note taking app Joplin (github.com)
Please see the ReadMe on Github for full instructions.
Thanks to CalebJohn for resolving an issue with this plugin for me, and the suggestion of v2 of the plugin that wouldn't immediately insert the tags, but dynamically render the highlights upon viewing the note.