The question as answer is "what is wrong with your data that you feel
the need to hide/distort information and distract from the story of
The hopefully thought provoking answer is "fortune(197)".
The answer to the question not asked that should have been is "No!
don't do that!".
If you have read all the above and are still determined to continue
despite warnings, then ...
The answer similar to handing a fully metal knife to someone poking
around in a plugged in toaster is "?rasterImage".
Well that answers the question as answer. So while you are working
within the system to get your company to change the policy you can use
rasterImage to add a gradient background to the plot, then use points
or lines or other functions to put the parts of interest back on top
of the gradient (if it is not obvious how to do this then give us more
detail of the types of plots you are doing, a reproducible example is
best, and we can give more detail on how to do this).
Looking at these, and in retrospect, if I were writing a manuscript of
the pre-digital age, I would definitely add a burning mark as a
finishing touch to complete the work. Perhaps waving the parchment
above a burning candle.
With modern digital support, you can fake a similar result using e.g.
grid.raster or rasterImage, as others have said before.