For others running into this without any of the above solutions working AND you have modified the default theme, you might want to check the highlight color for occurrences.
Preferences > General > Editors > Text Editors > Annotations
Then select Occurrences in the Annotation Types, and change the Color Box to something other than your background color in your editor. You can also change the Highlight to a outline box by Checking "Text as" and selecting "Box" from the drop-down box (which is easier to see various syntax colors then with the highlights)