Curtain Wall object materials

[Anonymous]

Even though I'm setting the material of the glass and the upper and bottom panel to the same glass material, I seem to always get a different shade of that in the rendering (even when there are no other objects behind it or in front of it)

I'm guessing it's something with the object itself, but not sure, any ideas?

[Anonymous]

object settings

[Anonymous]

object settings 2

[Anonymous]

I need to revisit this topic since I still haven't found an answer to this phenomena, it does however seem that when rendered with AC internal engine or Zbuffer engine only the lower panel is a different material! any ideas?