After magnifying the pic, it looks like Crews' fork is probably nickle. The down tube is rather dark looking and could be black but if you look closely at Crew's left crank arm, the chainstay right next to the crankarm is very reflective. Unless this was a very glossy black paint job, I'm gonna say too much reflection for paint so I think the frame is nickle plated also and that the downtube is not reflecting much at that angle. Since the Sentry was only available in nickle, this only makes sense. I don't think Patty Factory guys rode anything but nickle in races up until the last few batches of Long's came out with the modern font decals at the end of '82 or so. Those were the first chrome ones, IIRC. Brian later showed up with that yellow PR200 at the very end of Patty's existence and it seems like I saw a white one or two after that. The only other example of a painted Patty I have ever seen for sure(besides all the ruined ones) was the yellow Patty Long that Brent posed with in a Moto-X Fox ad before the PR200 came out.
Either way, since the Sentry came out in the late 70s and pr200's frame was made in '83 and is at least two generations ahead, painting his PR200 black because a Sentry MIGHT have been painted black is probably the wrong way to go if trying to keep things authentic. In my book, you have only two color choices for a PR200 if you are gonna paint it. Patty Yellow or white and I am really not even sure about white, TBH.