I served in Special Operations Command at Ft. Bragg. I was in 4th Psy Ops Group. I wasn't a Green Beret, or a Ranger, but I worked with lots of them. Good guys.
When it comes to the "whatever works" uniform policy, that doesn't extend to berets and "chest candy". They take those off when they're working. But no Green Beret would be caught dead wearing a black beret - that's what every regular soldier wears, there's nothing special about it. Stalker and Beach-Head, who both served in the Ranger Regiment, would wear proper berets as well. If they wore berets at all, they would wear the correct one. They EARN the right to wear those berets. It means a lot to those guys. I wore a Maroon beret for the Airborne - it's not nearly as exclusive as a Tan or Green Beret, but there's no way I would want to wear a black beret.
The "Hall of Fame" figures... I hear what you're saying, but it is Flint, and Duke, and Stalker. They were the first "deluxe" 12" figures produced by Hasbro of these characters. They set a precedent. I understand what you're saying, and I agree that I prefer for the 12" figures to more closely resemble the original figures. But even Sideshow Duke takes some suble liberties.