Help! My ducks are turning yellow!

I have noticed about two or three days ago that my two Pekin ducks (Thelma & Louise) are going from white to yellow. They have a distinct yellow caste and I am not sure why. They are about 12 weeks old (give or take two weeks) and have lost their baby feathers, where there was a distinct yellow, but became sparkling white. They are happy and healthy and eat chicken & ducks pellets (they share the same yard for now) We give them vitamin drops 3 x a week and apple cider vinegar every couple of days in the main waterer and they get a tb of liquid calcium every few days for shells and bones. They can free range from about 3-5pm or whernever it starts to get dark so they are getting bugs and whatever else id around. They also get Romaine and celery tops and whatever the grocer is throwing out that day. Has anyone had the same experience or know of someone that has? I would love to know what is going on. Are we giving something that we shouldn't or too much? Help!

It is my guess that the oil for preening is what is yellowing the ducks. Are they able to bathe their entire bodies? Even once a week? I let mine bathe once a day, but I only have one white Khaki Campbell and he is still white white. I did notice the turkeys are turning yellow though and that is my guess. I am sure some one who actually knows will have the answer.

That is Normal they will get white again soon then once a year you will see them get a yellow cast to them
If you were going to eat them it is better to do them before they get the yellow hue as now they will have more pin feathers

wheew! I thought that maybe we were slowly killing our big girls. No Joe, we will not be eating these big girls, they will be bred to my friend's Pekin Male in the Spring, whenever that is.