Those are Plymouth White Rocks...the king of breeds. They are so clean because their feather quality seems to just shed dirt...they have the softest, silkiest feathering of any breed I've ever touched in my life..and that's saying a lot. Their feathers are much like silk...light, soft, strong and resistant to soiling. I was just given a rooster from one of the most important WR bloodlines here in the US, or so I'm told, and I have two pullets from the next one removed, so I'm going to start breeding the two strains and move to just keeping WRs and also some Khaki Campbell ducks(that's an experiment in the breed to see if they will work out) for laying.
ah ha no wonder they look fluffy and like clouds. SOOOO pretty and good luck with your breeding!!!