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Double-sided materials
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Sometimes it is desirable to to draw the 'inside' of an object with one color, and the 'outside' of an object with another. The ``Set_Color`` command supports "sub-options" for face color which allow color to be set differently on the front and back faces of a surface or polygon. Here's an example::

	Set_Color("front = [color by value/name], back = [color by value/name]");

A bottomless urn with the front face color set to blue and the back face color as white: 

.. image:: images/0638a_doubleside_example.jpg

*Front and back color example*

Currently, this feature is not applicable to individual faces of a shell, but only applies to entire shells. You will only be able to see the inside faces if backplane culling is off, since 'inside' faces (those faces whose front-side normal is pointing away from the camera) would otherwise get culled away. 
