OpenGL 3D Object to DXF File

Hi All,
I am trying to write a DXF file from a 3D object which is constructed with polygons(triangles). There are more than 1lakh triangles generated by our marching cube implementation to re construct a human face. But when I am writing the same triangles in the 3DFACE ENTITY of DXF file, the same face (with colour and shading) are not coming. I have the following doubts.

  1. Is 3DFACE is the best entity to choose
  2. How can I represent Colour and Normal of each triangle

Please help me by providing some clue on this area.

Thanks in Advance