I only have my own experience but my cayuga/pekin drake hated my pure pekin hen and would bully her and refuse to mate with her. The cayuga/pekin hens were just fine with their pekin buddy, but the drake wanted nothing to do with her. The mixes were black with some white, and the pekin was obviously fully white.
Unfortunately even after a year of being together he still didn't like her. He wouldn't protect her from the chickens and would nip at her when she ate or drank while he was nearby.
All ducks are different, though, and I've seen mixed breeds with different colorations get along just fine also!