Chocolate should not be mated with Yellow otherwise pink nosed yellow dudleys can be born, but with another chocolate or a black is fine; the colour of the resultant puppies depends upon the genes carried by both parents, not necessarily the colours that the parents are. So in a choc to choc mating you could get any combination depending on what is behind the parents - and not necessarily in the immediately previous generation
Chocolate is not dominant and there does not need to be a black parent to produce black puppies.
Colour genetics in any dog is a complicated issue which can be investigated prior to mating.