There are two types of silver mutations: dominant (on the left) and recessive (right). Both types of birds have a silvery grey appearance, which is caused by a reduction of melanin (the material that produces greys and browns) in their feathers.
Recessive silver birds are uniformly silver-grey, with bright red eyes and pink feet and beaks.
A dominant silver cockatiel can be either a single-factor (it has only one copy of the affected gene) or a double-factor (it has two copies). Double-factors are lighter than single-factors, just as if they had a double dose of melanin reduction. Both types have dark eyes, beaks and feet, and a dark grey “skullcap”. This mutation is dominant to all other colors, including grey. See the genetics lesson for an explanation of the way in which this color is inherited.