It's tricky to answer a question like that with words, and a lot easier to answer it with a picture.
I did a quick Google image search to try to find someone with a good picture that shows newborn Cocker puppies in various shades of "buff". Here's what the best one I found:
Note the vast difference in color between the pup on the left (with the blue necklace) and the pup on the right (with the silver necklace). And if you look closely, under the mom's ear, you can see a third pup whose shade is a little less "red" than the one on the right.
Please note that when Julie Hydro talks about silver she is talking about a true genetic silver... a very unusual and rare thing. On my coat color page, when I talk about silver I am talking about how the term "silver" is commonly used in the real world of buying and selling puppies. 99% of the time when someone is talking about a silver colored Cocker, they are simply talking about a buff Cocker whose buff coat is not particularly red... a coat that is much lighter in shade than most "buff" Cockers.
Imagine you were the breeder of the litter of puppies in the picture above. How would you describe the pup on the left versus the pup on the right? I bet some breeders would say the one on the left is silver and the one on the right is buff. On the other hand, some breeders would probably say that the one on the left is buff and the one on the right is red!
The point is that there is nothing in the Cocker Spaniel standard that specifies the proper terminology... and that lots of people use lots of different terms however they see fit! So, it's always a little risky to rely on a text description of a "buff" Cocker Spaniel... and much more definitive to see a picture.