Initial thoughts
There are pair of white swan and pair of black swan. Why not one white swan and one black swan? In “Swan lake”, white swan is princess and black swan is evil. Why black swan has to be evil all the time? I am going to give the black swan a royal crown and made it the prince of all swan. The white swan is its partner. Therefore, they become the royal couple.
Digital sketch
To be honest, I know the crown on a bird’s head is not practical. Even I can glue it on swan’s head I am afraid it would fell. So, let’s assume the crown stays on top of black swan’s head by unidentified force. 🤣

Summary
I was thinking the black swan’s feather would be like raven’s. Raven’s feather has bluish and greenish sheen under sunlight just like the black rooster. However, after studying many reference photos, I realize that the black swan’s feather is simply black with lighter color on the edge (I could be wrong). Its beak is different than white swan also. The black swan has red eyes. But here I change it to black blue otherwise it appears more like an evil prince. 😅
Well, I hope you enjoy this couple.