Done! The voxel characters now have:

**Front side (facing you):**
- Black eyes at the top of the head
- White mouth at the bottom
- Brighter colors overall

**Back side:**
- Much darker (50% brightness reduction)
- No facial features
- Clearly distinguishable from the front

The front voxels use z=-1 (closer to camera) with high brightness, while back voxels use z=1 (away from camera) with 35-50% brightness, making it easy to tell which direction the characters are facing.