Tips:
In Navisworks, if you get the error that all the object of that dwg imported are same color (duct pipe…same color).
What you need to do is to open the original Xref CAD dwg file which have problem (example HVAC_00.dwg), then you change the current layer to layer 0 and color to bylayer, close dwg, then refresh naviswork. it's now done!