How Does iMSTK Handle Texture Mapping for Internal Vertices in .msh Files?

I’m working with a .msh file and applying a surface mesh with a pointwise texture map. The texture appears correctly on the surface, but the internal vertices seem to take the color from the (0,0) position of the texture.

Where in the iMSTK codebase is this handled? Specifically, where is it assigning texture coordinates (or default color) to internal vertices that don’t have explicit UV mapping?