Make faces transparent

Hey, i use BoxGeometry and want to make some faces transparent. Most of the stuff I found on the www was old and deprecated. Using geometry.faces[2].color = new THREE.Color(0xFF0FF00) did not work. I saw BoxBufferGeometry has a materialIndex property to change material. But can this be done with BoxGeometry? Would be nice if someone could light me here. I also dont find a lot about how to work with multiple materials with newer versions

Thanks in advance

Try it like so:

BoxBufferGeometry supports a material for each side of the box. This allows you to modify the transparency settings for each side.

Thanks for your reply, but I actually wanted to know how to do multiple materials with BoxGeometry not BoxBufferGeometry.
Because I need to change vertices of the geometry and I only know how to change them with BoxGeometry like so:

this.geometry3D.vertices[7].x = IIP.x
this.geometry3D.vertices[7].y = 0
this.geometry3D.vertices[7].z = IIP.z

Changing vertices with BufferGeometry is not as expected. See The face is loosing connection to the other faces and it openes a hole? How would I change vertices of a BoxBufferGeometry with same behavior as BoxGeometry. This is what I want when changing vertices

When I just created these fiddles Im noticing that multiple materials work same on BoxGeometry. This may be the solution