Have you ever had AEC objects set to display ByLayer but are the wrong color in xref in AutoCAD Architecture, MEP, Civil 3D and Plant 3D, check out this AKN article on what the solution is!

https://knowledge.autodesk.com/support/autocad-civil-3d/troubleshooting/caas/sfdcarticles/sfdcarticles/AEC-objects-set-to-display-BYLAYER-are-the-wrong-color-in-Xref-in-AutoCAD-Architecture-or-AutoCAD-MEP.html