Not sure how high sci-fi of a look you're going for, but out of personal taste...
I think the handle would look nice if it were wooden. Preferably a darker wood, and laminated. Maybe wooden grips on a gunmetal handle, if you can pull it off. The barrel holder (assuming that's the clitellum-looking tube around the gun barrel itself) should also be laminated wood with brass around the edges, with brass rivets just to look fancy.
The barrel, sight and trigger should be plain gunmetal black. If everything looked fancy, that'd just be clashy and it would look a bit homosexual.
The cord should be a shining/reflective, fluorescent gold or brass, something that looks like hot, glowing conducting a load of deadly laser charges and shit. The nut should be a dark red, blue, or some other color that looks cool and/or regal with bright yellow next to it.
