Unfortunately David all this is a matter of opinion and we can all have different opinions. Camouflage does help, that's why practically any wild animal will have it. Which predator you re talking about makes a difference too. A hawk can see a mouse from way up in the air. Supposedly an eagle can see prey from 2 miles away. Land-based predators can't see that well but they still have pretty good eyesight. A lot of then depend on other senses, like smell also. There are different things to consider.
I pretty much discount coloring/pattern from helping that much in chickens though because color/pattern is not the only thing that matters. A lot of these predators, especially the ones that hunt by sight, key in on movement more than anything else. Chickens have a lot of trouble staying still. Personally I do let any perceived camouflage benefit affect my choice of chicken color/pattern. From the chickens I've lost I don't think it matters.
As far as flying over fences there is a big difference in"can" and "will". Size does make a difference but many people would be surprised at how well full sized chickens can fly if they really want to. I've seen full sized chickens fly over a 4' high fence with over a foot to spare when they were trapped and wanted to get over the fence, yet that same 4' electric netting kept them really well contained. Unless they are desperate they don't want to fly over it. These same chickens fly up to a 5' high roost pretty effortlessly. I've seen some (including a large rooster) launch themselves form that 5' high roost, fly forward about 9', take a hard left, fly through the coop door, and land in the run. How well they can fly depends a lot more on how much they want to versus how well they can.
A 6' privacy fence will probably work really well at keeping them in. One risk is that they like to perch. It's possible if the top of that fence looks like a good place to perch they might fly up there just for fun. If they do that who knows which side they might hop down on. How likely is that? I can't put a percentage on it, either they do or they don't. If that happens to you one fix is to put some woven wire fencing around the top so it sticks up about a foot so they don't have a good place to land. But I'd try it without the wire first, it will probably work without the wire.
The 6' privacy fence will keep a few predators out, mainly dogs which are many people's main risk provided they don't go under it. Not sure what your privacy fence looks like. But you'd be surprised at how many predators will just go over it if they don't go under it. In spite of what you may have seen, from your location you are practically sure of having coyotes, fox, bobcat, raccoon, possum, and many others. Don't believe those stories about them only being out at night either, any of them can and will hunt during daylight hours. Nighttime is your biggest risk though since there is usually no human activity to scare then away.
My approach is to provide a predator-resistant space for them during the day and lock them securely in a predator-proof coop at night. They are still at risk but it's been pretty successful. How much risk yours would be at in your back yard is pure blind luck. People go years without problems in those situations, others are wiped out immediately. You just don't get guarantees with this kind of stuff.
I don't know what that coop you are getting from your friend looks like. Does it come with some kind of run? If not I'd suggest you consider building a fairly predator-proof run around it or attached to it. For four chickens it doesn't have to be all that big. That gives you a lot of flexibility in dealing with them. There can easily be times you don't want them roaming your back yard. Maybe you don't want them in your back pocket when you are doing something back there. Maybe you need to train them to lay in the coop instead of hiding a nest. Maybe they are pooping where you don't want them to, that happens a lot. Maybe a bobcat is picking them off one at a time and you need to lock them up until you deal with the bobcat. A lot of people start out with the idea that they are going to free range but later change their mind. The only way to find out though is to try it.
Good luck!
