Forced black faces using a mask is a nice idea but I do not think it is feasible, here is why.
1. There would be a massive lack of face variety, making everyone look the same, if you've been in a regiment a while you can recognize players by their face, not with masks.
2. Big faces would clip through the mask, looking very strange and buggy
3. Each mask would have to be part of the helmet which would have to be added onto each hat which wastes a lot of time (There are a lot of zulu hats, it's alpha with 2 units and theres about 12 hats so far)
4. Masks would be double the faces adding a lot more polys giving a lower fps.
5. It would make the zulus seem as if their heads were very big which would look weird.
I don't think it's worth it, if a regiment knows it will be playing Zulu they should choose black characters, otherwise you will have to accept it sadly.