Complex sentence: Their external feathers are white, sometimes with a yellowish tinge, although this is more obvious with ducks that have been raised indoors and not exposed to sunlight, rather than ducks that have been raised outside.
Split into simpler sentences: Their external feathers are white, sometimes with a yellowish tinge. This is more obvious with ducks that have been raised indoors and not exposed to sunlight, rather than ducks that have been raised outside.