Rebooted and loaded up an old scene pictured below.  Added a new wall sections (w/ niche) and added the marble texture, set normals forward in the material room.

Added a box primitive to the scene, added the same mat, left normals forward unchecked

Rendered and got these results.  Other Walls currently using the blue veined marble MAT.

Note the columns are using the same Marble Mat, except it was applied prior to whatever caused the problem, but they still render fine.

No Ambient Occlusion on anything.  Using the default 3 lights from Poser 6, Ground plane is invisible.  Light 2&3 have shadows turned off.

I have tried a new scene with just one wall, got the same issue.   Also, doesn't seem to matter which way I rotate the prop, the color effect is always on the side with the light source.

 

I don't intend to use the MAT file with the final release, was just playing around for testing.  I have not had any problems with any UV mapped textures or any other mat file I've tried so I'm puzzled what it is about the Marble MAT that is causing an issue.  I just don't want any issues with the final release and not knowing what is causing this is bugging me.

Here's a SS of the Marble MAT file settings if that helps.

 

I'm stumped on this one.