best and safest way I have found , is to buy permanent marker pens in the same colour (or slightly darker) as the plastics....
I have 2 different greys, 1 for the dark grey on the dash board and 1 for the lighter colour on the doors.
carefully follow scratch with marker, then rub in (off) with fingers. Repeat till happy with result.
Works for me...hope it works for you.........stay well everyone.