I think you may have a very dark black and tan pup. When born the black and tans can appear to be black. Generally the lighter they are , the more tan points , the lighter they will be as adults . Lighter meaning the ratio of tan to black , not necessarily meaning the pigment of the tan will be lighter.
Does the dam have a black recessive factor?
Even though the sire is black in order for the pups to be solid black the female would need to contribute a black factor .
This change of colour could continue well into the dogs second shed of coat -- into adult hood , perhaps 18 months to 2 years. The biggest change would be the puppy coats shed as adult hair comes in. After a year the changes would be minor.
Post a picture and a pedigree and I am sure some experienced people could give a guestimate of the pups future appearance.