Pearl or Opaline is a Sex-Linked recessive mutation which alters the pattern of how melanin is distributed throughout the plumage. This mutation also enhances psittacin in certain areas throughout the plumage, a good example can be seen under Lutino Pearl Cockatiels where as the loss of melanin shows us the concentrated psittacin pattern indicating the presence of this mutation.
This mutation was established in Germany in 1967 and is widely available around the world.
The Pearl mutation has many variants of patterns among Cockatiels and each of the strains of pearl can be enhanced or selected to a breeders liking. How different pearl patterns are reproduced and inherited are fairly inconsistent as offspring do not always mimic the pattern of the parents and this is naturally a result of variation, selecting strains of desired pearl patterns in gene pools and parting with the undesired patterns is the only way to try to establish a desired pearl pattern in a population.
Cockatiel males lose their pearl markings when they molt, as they mature their markings are covered over by the necessary melanin that indicates sexual maturity however there is an exception when combined with the Recessive Pied mutation as this seems to disregard the sexual dimorphic nature of the Pearl mutation enabling males to retain their Pearl. It is easy to mistake a pearl male for a normal male as they lose their markings when they mature where as females retain their pearl marking throughout their lifetime.
It is considered undesirable to pair Pearl to mutations such as Dominant Silver, Emerald and Olive as combinations of these mutations would produce indistinct colors making them hard to identify, this mutation is a favorite among many as this mutation is paired very easily to most mutations available with favorable colour combinations being produced with no contamination tacking place.