Hello there
There are quite a few posts with reference to this solid v parti-coloured thing already..
I have had a gold show cocker which I sadly lost earlier this year and currently own a blue roan pup. My gold dog was highly strung and had a lot of energy but a wonderful wonderful kind dog to own - my son came along when he was a one your old dog and he proved to be totally bomb proof with kids - because he trusted me and we had a good relationship before the kid came along. My new blue roan pup is a lot more laid back but is currently very bitey towards my now 5 yr old son, something all puppies do to a greater or lesser extent. Young children definitely inspire puppies to bite more too as they give all the right reactions - squeak,scream and run!. However, I expect my new pup to be just as kind a dog as my last was with the right handling and training.
I'm not sure what exactly the 'firm hand' is referring to in your book.. no pup is born 'bad' they all need to learn about how to interract with their human families and by far the best way to do this is by positive reward and consistant calm handling. Also avoiding situations that could cause problems - I'm currently keeping my puppy and son mostly separate until the pup is a bit older and learns not to attack my son every time he walks past.
Same as children, puppies don't learn how to be acceptable in our world over night it takes a long time. If they experience bad things or don't get socialised or introduced to new things in the right way, then they will react in a way that's natural to them; that we as humans, may not approve of. If a dog experiences pain or lots of shouty aggressive 'dominant' behaviour from us, it may well inspire aggressive behaviour in the dog.
Each dog, regardless of colour is unique and the key is knowing that you have the time, patience and are prepared to put a lot of kind hard work into your new charge and spend time learning about the best way to do it. Cocker's are not always the easiest dogs but they all respond to good training...
Good luck and keep us posted!
Hannah x