Rouen to pekin depends entirely on what the pekin duck has going on genetics-wise 'under' the white and it might end up being a lot of things. Most often, however, it's black bibbed, so ducklings from a rouen to pekin cross would be black bibbed if that was the case. You might end up surprised, though.
Rouen to welsh harlequin would result in ducklings that look just like rouens color-wise, only they will be carrying the harlequin gene, so if you bred them together or back to welsh harlequins, you could get some snowy offspring from them.
Also, the gold phase welsh harlequins get the gold phase color from chocolate. So any male offspring from a cross between your rouen and a gold phase would be carrying chocolate, too. Females would not inherit it.
