In an attempt to add this feature, I have added a little patch to the current (3.1g) POV-ray source. This adds the object smooth_color_triangle to a mesh object (and only to a mesh object). It is specified like smooth_triangle, with added colors (see the syntax specification below). 

• Download the modified files: pov_color_changes.tgz. If you do not have the source code, please get it from www.povray.org
  The modifications are labeled as /* AP */ or /* [AP] */

• Detailed look at the changes and the mechanism behind the patch

• Linux 386 executable (RH6.0 glibc2.1)
• SGI IRIX executable (IRIX 6.5)
• MacOS PPC version (kindly provided by Matthias Weber)

Please feel free to contact me about this patch at ansgar dot philippsen at unibas.ch

MESH_TRIANGLE: 
     triangle { <Corner_1>, <Corner_2>, <Corner_3> [MESH_TEXTURE] } | 
     smooth_triangle { 
     <Corner_1>, <Normal_1>, 
     <Corner_2>, <Normal_2>, 
     <Corner_3>, <Normal_3> 
     [MESH_TEXTURE] 
   } |
  smooth_color_triangle {
     <Corner_1>, <Normal_1>, <Color1>,
     <Corner_2>, <Normal_2>, <Color2>,
     <Corner_3>, <Normal_3> ,<Color3>
     [MESH_TEXTURE] 
  }