Blue (bl ):
Used for an autosomal recessive mutation with total absence of yellow psittacin in the entire plumage. Gene locus encodes for one, in some cases more than one component of the psittacin(s) residing and showing in the cortexes of the feather barbs and barbules.
The bl-locus is considered to be complex and therefore able to develop multiple alleles resulting in birds displaying psittacin colours in between the wildtype and blue, the latter being the most extreme mutant produced by this locus.
In the Budgerigar [Melopsittacus undulatus] there is evidence that the bl-locus has mutated in two different ways resulting in the same blue phenotype. This is unique for Budgerigars thus far.

Dark factor (D):
Used for an autosomal incomplete dominant mutation darkening the basic colour of the bird in the entire plumage. Gene acts in the feather follicles and suppresses the width of the spongy zone within developing feather barbs.

Dilute (dil ):
Used for an autosomal recessive mutant with black eyes, dilute pigmentation in the entire plumage and normal pigmented legs and toes. The genuine dil-locus is considered to be complex and therefore able to develop multiple alleles. Possibly involved in the development of dendrites, those parts of melanocytes through which they disperse their pigment granules into the growing feather barbs. Macro melanin globules (FKA macromelanosomes or giant pigment granules) found in cross sections of wingcovert feathers, are characteristic for this mutation. Gene probably acts in the melanoblasts (precursors of melanocytes) and affects normal dendrite development.

Fallow (f, pf , rf):
Used for autosomal recessive (non pied) mutants having ruby, pink, wine red or plum coloured eyes including a dilute or suffused colouring of the entire plumage. These mutants also have flesh pink coloured legs and toes and must definitely be classified as different types of albinism.
At least two different gene loci (other than the a-locus) have been recognized in psittacine birds. These loci are possibly involved in melanosome matrix protein production and are of major importance for the development of melanin granules. All known autosomal loci other than the a-locus producing fallow types, have not been able to develop any multiple alleles thus far. Gene acts in melanocytes and has pleiotropic effects in ruby eyed fallows such as high mortality rate after hatching and inborn weakness.

Dominant grey (G ):
Used for an autosomal dominant mutation suppressing the formation of the spongy zone including the medullas of the feather barbs in the entire plumage. In absence of the spongy zone no blue interference takes place giving a blue series bird a grey appearance or a greenseries bird a grey-green appearance. Grey-green birds are sometimes mistaken for olive green or the recently discovered mustard green. Gene acts in the feather follicles.

Recessive grey (g):
Used for an autosomal recessive mutation altering the complete or partial internal structure of the feather barbs through the entire plumage resulting in a grey phenotype in the blue series and a grey-green phenotype in the green series. At least two different types of recessive grey have been recognized under which English recessive grey, the type that affects the complete internal structure of the feather barbs (considered to be extinct) and Australian recessive grey, the type that only affect the medullas of the feather barbs, both recognized in Budgerigars. Recessive grey mutations in other species are to be investigated. The nature of the gene products in these types of grey is unknown. Gene(s) act probably in the feather follicles.

NSL ino (a):
Used to designate an autosomal recessive mutant showing a complete hypopigmented phenotype and red or pink eyes. This gene locus, also known as the c-locus in mammals, encodes for tyrosinase, a copper containing enzyme that catalizes the production of melanin within melanocytes during an early step in melanogenesis. The "c-locus", which we have designated as "a" for birds, is able to develop multiple alleles resulting in less extreme mutant phenotypes which should be classified as pink eyed fallows having greyish-brown flights. Gene acts in melanocytes and only affects melanin production, not psittacins.
To test if a known fallow mutation is allelic with the NSL ino in a certain species, it is recommanded to cross breed all known different types of (red eyed) fallows within that species with the NSL ino of the same species (if available). If all the F₁ offspring has red eyes, the used fallow type is allelic with the NSL ino, if the F₁ offspring are all (blackeyed) wildtype birds, than we have to deal with a separate mutation residing at another locus.

Mottle (Mo):
Used for mutants developing progressive piedness after each moult resulting in unstable nonuniform pigment patterns. This delayed amelanosis, also called vitiligo, is a trait of the autoimmune system causing local cell death and destruction of melanocytes. In a genuine "mottle", wingcovert feathers are often the most sensitive and, affected areas will not recover. This trait may or may not proceed during the entire lifespan of the individual. In birds two different types have been observed. Gene(s) act(s) in melanocyte surrounding tissues.
The inheritance appears to be polygenic and is a subject for further research.

Pied, Piebald (Pi, Pb):
Used for mutants with a dominant inheritance showing nonuniform pigment patterns in their plumage. Eye pigmentation in these mutants is always unaffected. There appears to be evidence that at least two dominant pied types can be distinguished from each other in an early stage by observing the colour of the down. The piebald type, like the Australian pied in Budgerigars, has grey (wildtype) coloured down whereas the Dutch pied type in this species has white down. This is only so if one has to deal with non-opaline birds, for sex-linked opaline specimens always have white down.

Recessive pied (s):
Used for mutants having a non uniform pigment pattern with recessive inheritance. Eye colour in this type of pied is affected and Anti Dimorphic effects (ADM) also have been recognized. Gene acts in the neural crest and is possibly involved in melanoblast development and differentiation. As a combo with Dutch pied (Pi) in Budgerigars, these loci interact in such way that the result is a completely hypopigmented bird with dark eyes also known as a dark eyed clear (DEC).

Spangle (Sp):
Used for a autosomal dominant mutation in the Budgerigar (Melopsittacus undulatus) suppressing pigmentation of the wings in such a way that the pigment pattern appears to be "reversed" which is definitely NOT the case.
DF birds are almost completely amelanotic and sometimes look like dark eyed clears which they are not, for abnormal pigment residues and abnormal melanin clustering can be found in cross sections of breast feathers. The site of the gene action is still obscure and subject for further research.

Sex-linked ino (ino):
Used for the sex-linked recessive mutant showing a hypopigmented phenotype and red eyes. The gene locus is presumed to be involved in controlling tyrosinase transport and/or morphogenesis (modelling) of pigment granules. Sex-linked ino mutants do have a very much increased tyrosinase activity and often show ghost patterning on their plumage. Gene acts in melanocytes and is not able to delete brown eumelanin in cinnamons completely.
This locus is known to be able to develop multiple alleles which manifest themselves in some species as incomplete "back" mutations also known as par-inos or semi-inos AKA pallids. This phenomenon is hypothesized to be the result of the departure of a transposable element, also known as "jumping gene", from the sex-linked ino-locus which sequence has been proven to be very much in favour for such elements to "jump" on. On departure of the transposable element it will leave its "footprint" behind preventing the gene to restore completely, resulting in a much less dramatic phenotype somewhere in between the wildtype and the ino. The colour of the flight feathers in pallids varies from black in Budgerigars (Texas clearbody) till "dirty" white to irregular grey or greyish (never brown!) in other species.

Sex-linked cinnamon (cin):
Used for the sex-linked recessive mutant displaying cinnamon brown eumelanin instead of black in the entire plumage. Eye colour is red at hatching and darkens with age to almost black. The colour of the legs and toes is flesh pink. Gene possibly encodes for a second tyrosinase related protein, acts in melanocytes during an early step in melanogenesis and is able, after crossing-over, to express itself in combination with the sex-linked ino. These "combos" should be called cinnamon-inos in general. There may be one exception to this rule; in Budgerigars such combo is called "lacewing" because only in this species their striking phenotype justifies this name.

Sex-linked opaline (op):
Used for the sex-linked recessive mutant showing a "shifted" colour effect streaming downwards from the head, saddle, wingcoverts and tail feathers. The opalescence effect is most striking in Budgerigars and unfortunately less obvious in some other psittacine species.
The op-locus affects the colour of the down which is eg white in the Budgerigar and yellow in Agapornis roseicollis in opaline birds and grey in wildtype birds. Gene is presumed to act in the endocrine (hormonal) system.

Less known mutations

Brown or brownwing (sepia) (bw):
Used for an autosomal recessive mutant producing sepia brown eumelanin instead of black. Gene locus could be a possible candidate for the production of a tyrosinase related protein acting during a late step in melanogenesis.
Presumably identified in the brownwing Budgerigar, is under investigation. Gene acts in melanocytes.

Blackface (bf):
Used for a melanistic mutation in the Budgerigar (Melopsittacus undulatus) with recessive inheritance reported twice. Only few specimens do excist at present. Gene acts in melanocytes. Further research is recommanded.

Clearbody (Cl):
Used for an autosomal dominant mutation suppressing the complete internal organization and structure of the feather barbs in the entire plumage. Feather barbs are almost solid keratin, have poor developed barbules and are sparsely populated with small structures that could be interpreted as incomplete medullary cells sometimes containing few melanosomes (pigment granules). The cross sections of feather barbs taken from the breast and the lower abdomen of dominant clearbodies, look like cross sectioned icecicles. The normal pigment pattern on the wings and head is unaffected. Gene acts possibly in the dermis (skin).

Faded (fd):
Used for mutants showing a slight pigment dilution with autosomal recessive inheritance. Gene probably acts in melanocytes. More research on these mutants is necessary.

Misty (Mt):
Used for mutants showing a slight pigment dilution with autosomal dominant inheritance. The nature and gene action in these mutants is unknown and yet to be investigated.

Slaty (Slt ):
Used for an autosomal slaty coloured mutant with dominant inheritance. These mutants have a very intense black pigmentation of the flight feathers and a slaty body colour in the blue series. The nature of this mutation is under investigation. Gene possibly acts in feather follicles. The name slaty was chosen to distinguish this mutation from the sex-linked slate Budgerigar.
The mutation has only been discovered in Agapornis Fisheri and possibly Indian Ringnecks thus far.

Sex-linked slate (sl):
Used for a sex-linked recessive mutation altering the comlete internal arrangement of the medullary cells, the pigment granules and the spongy zone within feather barbs of the entire plumage. This mutation is unique for Budgerigars and has never been encountered in other psittacine species thus far. Gene acts in the feather follicles.

Hope this page will be of any value for those who have difficulties in identifying and understanding mutations in psittacine birds.