When set to Surface - Colour Fill, the 3D document will display the Surface Colour of your material, in this case, Concrete 04.
If you do not wish to change this, you could add a rule to your Graphic Override which will override the pen colour of your desired floor planes. eg. If a slab uses the surface Concrete 04, set Fill Type to foreground and set Fill Foreground Pen to white. Also ensure that the surface type override Cover/Uncut is enabled.