I have just read on KC website black&yan satffies are highly undesirable. The pup i am buying is adverties as a black brindle (form a breeder) i noticed it was predominantly black but with small flecks of tan is this what they are referring to as undesirable?

Don't worry - your pup sounds by your description to be a correct black brindle. By black and tan they mean black with tan markings like a rottweiller or dobermann.