How do I add custom gentials to animation rigs?

[melancholydeviance]

Hi! Sorry if this is the wrong place to ask this, but I can't really find any part of the forms dedicated to animation help specifically.

Anyways, I've been having a problem with putting custom genitals onto rigs.  I've found out how to add new meshes to a rig by exporting the mesh via S4S, and append them in blender so they work and are connected to the model. However the meshes always show up gray with shorts/underwear on, both in S4S and blender. Is there anything I can do to fix this or is there a better method of adding genitals to rigs.  Images below of my attempts to grab a vulva mesh and penis mesh, and of how they look in blender.