How to Get Rid Of Nasty Back Ground Green
Storm alerted me to "duplicate code" .... this was in itself a false positive. Nevertheless I have this nasty background green. I have looked, and looked, and tried removing from inspections everything that looked appropriate to no effect.
Please put me out of my misery - how do I get rid of this. Many Thanks!

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Hi there,
Place caret at such text, then invoke Ctrl+Shift+A (or whatever shortcut you have got there for "Help | Find Action...") and type "jump to colors"
You need to invoke "Jump to Colors and Fonts" action:
It will show what styles are used for the element under caret so it's much easier to identify what style to alter.
For example (my caret is on "doSomething" function name -- how it normally looks (caret is elsewhere) and after performing the aforementioned steps):
You may also check what inspection does it. Place caret on the issue (ideally on first few symbols), Alt+Enter to invoke Quick Fix menu (on Mac it might be different key instead of Alt) and look from there -- pressing "Arrow Right" while on a inspection/quick fix allows to show extra submenu with very useful actions (can also be reached using a mouse, but the area to click is rather small):
Thank you for your rapid reply. I might have found a bug. I tried everything you suggested without success. Possibly because my problem was not directly related to a specific word, but rather the background. The Fonts and colours dialogue reported the background as being black, which it clearly was not. So, in desperation, I simply cut the code out of the page. The green was now gone. Then I pasted the code back in, and still the green was gone, and normality was restored.
BTW - I think I have seen you on SO as well under the pseudo name of "lazy one" . Correct? :o)
Thanks.
In general, it could be https://youtrack.jetbrains.com/issue/WEB-40442 or one of the linked tickets. Indeed, Cut and Paste seems to help in such cases.
P.S. Almost, it's LazyOne.