PROBLEM:
Elevation or section views look transparent.
Also Visibility/Graphic settings may have no effect.
CAUSE:
There is a DWG visible in the view that has its insertion point more than 20 miles away.
SOLUTIONS:
Remove the offending DWG.
Hide the offending DWG.
Edit the DWG so its insertion point is not so far away (you may need to re-position the DWG in Revit).