Funny thing is that we had a flock of Light Sussex and I wanted to put some marans into their pen, we moved them all to new territory so no-one would be 'at home' and then watched them. Mayhem! The sussex attacked the marans and shooed them off. We removed the marans and thought again and swopped some older light sussex and put them in with the others... nothing, peace, they all got on! Hmm I don't want to think that my chickens don't like dark chickens but it does seem to be the case? Maybe they couldn't tell the difference between the new light and the old? Hmm

But off the subject a bit there, be careful, sometimes they will never get on and you will need to pen each away from the other or one will end up dead.