I have no idea why the black ones are the ones being picked on. It is starting to seem more than a coincidence from the way you describe it. Some breeds are more docile than others and may be further down on the pecking order. Buff Orps have that reputation and it is true in my flock. It's the only thing I can think of as to why black is the preferred color.
You have 144 square feet in your coop. By the normal recoomendations on this forum, you should only need 104 square feet for 26 chickens, so you have about 40% more coop room than you should need. You have 260 square feet in the runs which exactly meets this forum's normal recommendation of 10 square feet per chicken in the run. Since they are two separate runs, maybe something in the configuration makes them less effective? I don't know.
Boredom can cause this type of behavior. You might try hanging a head of cabbage or something they can peck at, especially if they have to jump a bit. Maybe add a couple of places for them to perch or maybe something they can hide behind. Maybe throw some scratch on the ground where they have to scratch to find it.
If they are too hot they can get aggressive. Make sure they have some shade to escape the heat if you have had weather anything like i have this summer.
One or two extra places for food and drink might help cut down on conflicts. Bullies will keep other chickens away from the prime food and drink places. Having extras cuts down on potential conflicts.
It is probably one or two hens that are into feather picking that are causing the initial damage. Chickens are cannibals and if one is imjured and starts bleeding they will all eat her alive. If you can identify the one or two causing the initial problem, take them out of the flock for about a week. When you put them back with the flock they will have lost their place in the pecking order and will be so busy trying to regain their social position that they may quit picking on the others. If you can identify the troublemakers and removing them temporarily does not work, you may be better off removing them permanently. I had to do that with an egg eater recently. I did not enjoy doing it but my flock is better off without that egg eater teaching my other hens to eat eggs.
Lack of sufficient protein can cause them to eat feathers. 16% layer should have enough protein if that is all they are eating, but if they are eating a lot of other food instead of just layer, you may need to add extra protein.
That's about all I can think of. Sometimes it is not an easy problem to solve. Good luck!