I am interested in making some new jewelery based on rings and amulets found in the game. However, I can't figure out how to change the gemstone color since it is apparently not a part of the texture- all different types of jewelery use one of four generic textures: silver ring, silver amulet, gold ring, and gold amulet. Also, it doesn't seem to be defined in the mesh file (at least as far as I can tell). The colors do show up in NifSkope without the texture loaded, but I have no idea how they are determined.

For example, let's say I wanted to make a silver ruby necklace. Would I have to use the mesh for the gold ruby amulet and just change the texture to the generic silver amulet?

But what if I wanted to make a new type of gemstone, like citrine or onyx? How would I change the stone color?

It is defined in the mesh: the Vertex Colors, in the NiTriShapeData block.

Like Madcat said, the gemstone and the metal (gold/silver) parts are assigned colors in nifscope. Highlight the Nitrishape data in the block list on any of the necklaces, look in block details and expand the vertex colors. You'll see the color shades when you expand. So the gold vertex colors in the gold ruby necklace could be changed to silver by changing the value of the vertex colors to match that of the silver necklace etc.

Thanks for the description.

Is there any way to do a global pattern substitution in a NIF file (i.e. replace all equivalent color strings at once)? At a first glance, it seems like Niflib or PyFFI might be what I'm looking for. I have some experience with Python and none with C++ so I'd prefer to use the latter. I'm currently looking over the documentation to try to find if a substitution feature exists.

It's much easier to open the nif in 3ds Max or Blender, and change the vertex colors from there, without having to resort to changing 100's of lines by hand.

Plus you can also smooth the mesh and so forth.

Btw, you can use the meshes I've designed for http://skyrim.nexusmods.com/mods/27038/? as a starting point if you want.