I agree you should change the food. That looks very suspicious of a nutritional issue. Unless it's just the lighting in the pic, his bill is much paler than what I'd hope to see on a healthy Pekin. Just as a basis for comparison, you can look at the pics from duckies1230 and the one Deb uses for her avatar. They have very bright orange bills, and that's what you want to see.
I'd also supplement the feed with some treats that are high in xanthophylls. As far as that goes with things ducks are likely to eat, I'd try leafy greens other than spinach, peas, bell peppers, carrots, corn and squash. You want to go easy on the corn this time of year or you may end up with a very chubby drake.
I would also, just a a precaution, wash his bill off with a soft cloth and some warm water, then put a thin film of Neosporin without pain reliever on it. It would be best to apply the Neosporin with a qtip so you can kind of paint it over the whole bill and still avoid getting it in his nares (nostrils).
Yes, his bill is pale. He's a very picky eater so it's hard to get him eating the right things. I'll change his feed, give him some good treats and keep ya'll updated. Thanks a bunch!