By Garry Stockton
One of the new features embedded in the Revit 2018.2 patch upgrade is the ability to change how your fabricated elements are shown. As below with Supply and Return ducts..
Visibility / Graphics Overrides on MEP Fabrication Elements can now be colour coded by applying a solid surface pattern in view settings. Select Filters and the required Duct (or any element), in the patterns select override and the fill patterns dialogue box appears. Pick your colour, then change the pattern to solid fill.