WOW! that color change is really neat--- like a duck that changes it's coat in the autumn years!
I originally just wanted to post that many purebred cayuga ducklings have a blush of yellow across the chest that becomes speckles of white in their adult plumage. It's not "desirable" for the show ring, but still very pretty. I got my first cayuga hen (Sneetches) as a feed store baby. She had a lot of yellow on her chest as a duckling, but I picked her for the black feet, hoping she was a cayuga, but accepting of the fact that she may have turned out to be black swedish and my gamble paid off. She has a little shooting star of white on her chest (She is after all, a Sneetch, with a star on thar!)
I had Ideal add 2 cayugas to my gosling order this winter and one was a tiny all black little girl with no yellow on her, and one turned out to be an EXTRA large boy with a splash of yellow... he was often larger than the smallest gosling when they were all in the brooder! We call him Big Ben now and he looks like his chest is frosted. The female (Betty) is still on the small side, but just about perfect example of the breed in almost every other way.