It might be certified but Allplan, as well as ArchiCAD as well as VectorWorks (I have not tested others) do write the color into the object AND into the material of the object. But these programm write different colors for the object and for the materials. For sure for Allplan the problem is NOT between stair and keyboard. If have found the problem and the ifc management knows the problem. I can not speak for others since I do not use ArchiCAD and VektorWorks but I recive IFC with this problem on a weekly basis and from different Architects.
cheers bernd