Color mutations occur on three aspects of a cockatiel:
Color: Aside from the normal grey is the change resulting from a mutated gene that affected the melanin or lipochrome of the bird.
Pattern: Is a result of a partially suppressed distribution of melanin to the body plumage.
Facial: Is a result of a reduction and/or suppression of Psittacin and/or lipochrome to the cheek patches or facial mask.
Solid Color Variations:
Solid color variations are mutations that affect the overall color of the bird. The variation in the deposits of these pigments and genes is responsible for the visual differences between the mutations.
Many mutations retain the normal characteristics of dark eyes (consists of a black pupil, and brown iris), pale grey to black beak, pale grey to black feet/skin and dark or black toe nails) of the Wild-type cockatiel. The Cinnamon mutation will have brown toenails, and a slight brown wash to the beak color, and upon hatch red/plum colored eyes that turn dark within a few days, yet retain a wine colored pupil. Lutino, Fallow and the Recessive Silver mutations have pink to red eyes, pink feet/skin, white (clear to pink) toe nails and pinkish/white to horn colored beaks.
Not only does an altered gene affect the body plumage it can also affect the natal down. Many times the mutation can be determined when the chick hatches. All the normal orange cheek patch mutations will have yellow natal down. The yellow down is a result of the lack of melanin pigment to the down. The Whiteface mutation down is white as a result of the lack of both melanin and lipochrome pigments. Split to Whiteface and Pastelface will have diluted yellow, off white down. I have observed that Emerald will sometimes have a dirty yellow-grey down, and Dominant Silver will have a grey tint to the yellow down. Eyes color can also give a clue to the mutation, which may be due to lack of, or suppression of, melanin per specific mutations.
Chicks and juveniles of both sexes will feather out with the female coloration. The young of both sexes, excluding pied, display the following:
1…Horizontal yellow stripes or bars on the outer side tail feathers.
2…The primary flight feathers will have yellow spots (dots). On rare occasions, a chick will feather out with no wing spots. I have seen this with a few Emerald, Dominant Silver, and the Incomplete patterned Pearl. When this is occurred the bird was always a male. Sometimes, but it is not 100% accurate, you can look at the wing spots and determine sex when a baby feathers in: http://tinyurl.com/9hedvzb
3…Solid colored crest and face, with a dull orange cheek patch, of the Normal Grey and appropriate color cheek patch for the specific mutation. Some young cockatiels of both sexes may also show a little yellow around the beak, nares, and forehead. The beak is light colored until 3-4 weeks of age and then it may gradually darken.
The first molt occurs between 5-9 months of age. The female will retain the same coloration throughout life. The male will molt the barring to the tail feathers and the spots to the wing flights. Actually the barring and spots not present after the first molt are a result of increased melanin masking them. The melanin pigment decreases on the head as the cock matures which allows the lipochrome pigments to become visible to the facial mask.
Note: The solid color and Pearl variations are Sexually Dimorphic, which is the phenotypic (or visual) difference between cocks and hens as they go through a molt and mature. Pied is Anti-Dimorphic, meaning that there are no visual differences between the hens and cock.