If the breeder is any good they will be able to tell you the colour of the puppies. What colour are the parents, and are they registered? What is the kennel name? Do you particularly want sable puppies, or do you want black and tan? Please ensure the parents have been hip scored, and the father tested for haemophilia.
Sables tend to go lighter as they get older, although a very dark sable will remain fairly dark.
I suggest you visit some other litters and have a chat with some breeders about what you would like. I can put you in touch with some reputable breeders if you let me know roughly which area.