Those in the know know that the D3DRS_COLORVERTEX Render State, present in every version of Direct3D since at least version 5, is not found in WPF 3D.
The question is: How can you approximate colored vertex data, with gouraud shading, using WPF 3D? Optimally, I just want to be able to assign an RGBA color to a vertex. And presumably, I'd define some kind of light or texture to accomplish it.
Some have suggested doing this with textures based on a LinearGradientBrush, but the interpolation done by the GradientBrush types doesn't really match the shading model I was hoping for: a linear blend of all three colors on all three vertices in any triangle, by associating an RGBA color with each vertex.