I don't know how to set mount points actually, I guess I'll have to learn that as well.
Well that'll do it. It's literally coloring the gun a specific color on the handle. (You'd do this with all of the materials, assuming you've been setting them and know what they are.)
Here's a Dropbox link that has several pdfs and refs that I used to learn what to do:
Here. I have no idea what the hell actually happened to the official link for it.
I've used this to make several weapons (them being within the guidelines but had issues like similar items already existing, so only one was approved) and several props that were approved.