why is my duck color different?

[TheBeardie]

I got my drake at a farm sale two maybe three years. He was all black when I got him, not a bit of white. Then a few weeks later he got some white feathers on his wings. Then slowly his head started to turn white
This is from about a week ago

And a video

This is him now

Why such a dramatic color change?

 

[Wyandottes7]

Almost all black breeds of duck slowly develop white plumage as they age. My guess is that this is just his natural progression of color change.