Ok if it an eclipse male ( eclipse plumage is a molt and during molt the males look like hens and then regrow their male plumage ) then he would be fertile and this usually happens in the spring when birds are breeding, when was this pic taken? It also could be a vey young male. Or if its a transgender hen it would be a hen that is growing male feathers and has raised testosterone levels and once could have been fertile but will soon not be. That is a normal colored mandarin in the supplied picture I know that for a fact. It may be split or offspring from a black mandarin but that specific bird is normal in color. The beak color also suggests young male or transgender hen. How old was the duck when pic was taken? A fully mature males beak is always red, a fully mature hens beak is always brown ( unless it is the strain of red beak mutation hens from Korea, which are extremely rare, and I don't believe are in the us yet. ) the picture of the darker hen would be nice to see as well.