Issue
When you set a view in Revit to the realistic visual style materials and decals are not visible.
Solution
Materials will not be visible with the realistic visual style unless Revit hardware acceleration is enabled.
To enable Hardware Acceleration:
Options > Graphics > Graphics Mode > Use Hardware Acceleration (Direct3D).
If you can't enable Hardware Acceleration it means your Graphics Card and/or Graphics Driver version is not supported.
AutoDesk link to list of supported Graphics Card & Graphics Driver versions is at: