I know what you are talking about. There are a few of my buffs that are absolute angels even after being in with all the other chickens (I have 50 something in one huge 65,000 sq ft outdoor pen with hen houses/brooders/roosts etc). These buffs are the only ones like this and are prone to loner...
I've noticed red chickens like everything from Red Stars to New Hampshires to Rhode Island Reds to even Buff Orpingtons have a "feral" potential. This goes from a willingness to go off alone and solo free range to being mean to other chickens - when I witness extra mean behavior toward another...
That is possibly good information - I would love to experiment with that then by using a rowdy red new hampshire rooster and crossing that with say a tame red star type hen to see if the chicks are less aggressive like their mother. A worthy experiment.
Aggression in chickens is mostly genetic - there are breeds that are just more aggressive. Reds tend to be more aggressive to where they peck at my hands more and such while feeding them and they also peck at other chickens more than say Orpingtons or Giants who are tamer by nature. I know...
Need to repost them now that they have all their feathers. Can't tell very much from the color of the baby downy fur. Black Jerseys are black fur then feather in all white.
Taming is best done during the first two months. The earlier the better. Teaching an older chicken new tricks is very difficult. Some people say that after a year you cannot even change their coop/henhouse with much success because they have trouble learning to navigate new designs after that...