
True Rage Syndrome (there is no such thing as 'Cocker Rage Syndrome') is rare and is not just found in Cockers. If you find a good, reputable breeder who breeds for temperament and type you should not have to worry about this. Cockers can be stubborn, strong-willed and vocal (i.e. 'grumbly') little dogs and Cockers with issues that would be (correctly) labelled as resource guarding, fear aggression etc. in other breeds tend to be stuck with the 'rage' label when in reality it is very rare. Regarding colour a well bred and well brought up solid coloured Cocker is no more likely to have behavioural issues than one of any other colour. This is a good article, although it is about Springers the points are still relevant
http://www.essfta.org/Health_Research/aggression.htm The Cockers Online forum is an excellent place for information on all things Cocker related. I have working Cockers myself but being a moderator on the aforementioned forum and having lots of friends with show Cockers I know that a well bred and well raised show Cocker is a great little dog and they make fabulous pets for the right homes.