I'm certainly no expert on color genetics, but I'll give it a try here...
I believe that the gene for chocolate is recessive, as is the gene for barring. These genes aren't competing with each other, they are completely separate. You can have a chocolate duck with barring, or a black duck with barring... Maybe even other colors with barring. Again, I'm no expert.
Also, barred and rippled are 2 different patterns, controlled by different genes. But rippled is recessive, too. So the explanation remains the same.
If you breed a chocolate to a chocolate barred, you will not get any barred ducklings in the first generation. Assuming of course that the first duck, the chocolate, is not carrying a single, "hidden" gene for barring. And the only way to know for sure is to breed them. If half of the ducklings are barred, then the unbarred parent is carrying one copy of the gene for barring.
Another thing about the chocolate gene. It is sex-linked. A chocolate drake will produce all chocolate female offspring. The male offspring will not be chocolate if the mother is not chocolate. Instead, they will carry the chocolate gene, but it will not manifest itself as visible chocolate coloring.
Now, how this relates to the fact that the birds are pied is a mystery to me. The only thing that I know about pieds is that they are actually white birds, with color showing through. I don't understand how that works from a genetic standpoint.
I hope that was helpful to you. And if anyone sees that I got any of that wrong, please correct me!
Oh, and also, not sure what you mean by a "normal" hen? What color is normal? LOL