I don't know much at all myself on the Dun genetics though. However, I know that it can be at times sex linked, but also not. It works the same as BBS. With Chocolate, Khaki(dun) and black. The khakis are like splashes, they'll always breed true, but over time can get washed out. Chocolate to Chocolate will produce all these varieties (at least in our bantam polish). So the birds you pictured as the duns look to be khakis to me? I know that in some breeds such as silkies it's pretty common for people to cross them with blues and get a fourth variety called mauve, at least to my understanding. Please correct me if I am wrong. I enjoy seeing these photos, thanks for sharing.