In the American sable cocker you are correct but to my knowledge the English sable cocker is different . This was proved after I sent samples to Scientists in America who were very confused to say the least . The have worked on my samples and that of a kennel in Sweden and have now located the Agouti gene responible for the sable colour in the ECS .
For example if I were to clip my sables back she would almost look golden/red in colour . There are some hairs that are totally black on the face , ears and back so she couldn't be clipped and mistaken for red though .But most of her back hairs begin red coloured for a cm or so and then shade darker until they are are black .
I almost totally hand strip her because if I cheat and use thinners I cut off the black ends and she looks a mess .
Here is a quote from Sweden
"Almost two years ago our new import finally arrived to us. As his name was Cardamine The Sable King our children soon began to call him “Kungen”, a Swedish word meaning the king. Kungen was also an English Cocker Spaniel, as our other dogs, but he differs in that regard that his colour was sable, red with a black “saddle”. In the saddle, each individual hair is bicoloured, black on top and red closer to the skin. This sable colour would make our minds busy for a long time forward. "
Sables seem to go grey on the head quite young , this is a mystery to me .