I'm voting Slide in Black, Frame in Matte Nickel, and Controls Black.
Your sight picture will appreciate the Black Slide, the Nickel on the Frame will resist handling wear.
Controls to be left Black for Contrast and easier recognition.
Frame Color Options
OD Green on the Frame is another possibility, if you want the GI look, but only if you live in an area where there is Forested area. If you are in a Desert Area, then the Desert Sand color on the Frame makes more sense. Trouble is, your buddies Witness is set up that way and you probably want something else to be different. How about matte Robin's Egg Blue on the Frame?