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Bio-Bum from over at the FacePunch Forums has released a white Phys Gun model that comes with the custom beam shown below that changes color.
This is a white physics gun. I had originally made the skin for the physcannon, but I hadn't released it (I might if anyone still wants it). Also, it has a custom beam that by default, constantly changes colors very fast (so does your original beam, though). I'm pretty sure that I had put the correct files and folders into the zip file, but tell me if I hadn't. Comments or suggestions are welcome.
See below for download and screenshot.