White muscovy ducklings have black on head?

[Jaybay15]

My white muscovy ducklings had a couple with black spots on head. Now they are getting their feathers they all have a little black on their heads. Does this mean they are not pure white? Will this black go away as they age?

 

[sourland]

They will probably have some black feathering on their heads for life.

 

[Jaybay15]

Thank you