Fallow is very similar to the cinnamon, and they are hard to tell apart unless you have them side-by-side. Fallow is the same dusty brown color, though fallow tends more to the yellowish side than the cinnamon’s brownish color. The main difference between them is that the fallow colored birds have deep red eyes. At first glance, and even on close inspection, it often looks like the normal dark eyes. But get them in the right light (often a camera flash will bring them out, but look for a red IRIS, not the red pupil that happens in any colored eye hit with a camera flash!) and you will find they are actually a dark red color. The fallow always has a pink beak, and pink feet.
Fallow is probably a lot more common than it is made out to be, as most fallow cockatiels are labeled as cinnamon, until someone notices their eye color (which often is never noticed!) the colors and markings are the same as for the cinnamon.
Silver is rather complicated. There are actually two different versions of ‘silver’ in cockatiels (Dominant and Recessive), and then you can get both single and double factors out of the Dominants!
The Recessive Silver mutation is a diluted or silvery grey version of the normal grey. The Silver has red eyes, a pink beak, and pink feet. Male Silver Cockatiels often have a very deep yellow face and bright orange Cheek Patches at maturity. Female Silver cockatiels will retain their immature coloration and the barring of the underside of the tail.
Dominant Silver is a mutation that is dominant to other mutations to produce a silver or light grey. The most obvious difference between the Dominant and the Recessive is the the Dominant has dark eyes verses the red eyes of the recessive. The birds can carry the dominant gene on one or both chromosomes, with the coloring effect being more pronounced in double-factored birds. When the dominant silver gene is carried on one chromosome, it is single-factored and the single factored is darker. When Dominant Silver gene carried on both chromosomes, it is double-factored and is a lighter grey.
Both dominant and recessive silver have the same face/sex-linked colors as the normal grey. The mature male will have a bright face and plain tail, the immature bird and the mature female will have the dull faces and barred tails. They all have the white wing stripe and spots on the flight feathers.
Olive is also called Emerald, Spangled or Suffused Yellow. This mutation is hard to describe and has to be seen. The term Emerald or Olive is a bit misleading though. Cockatiels do not carry any green pigmentation, so they can’t really be green. The combination of yellow and grey along with the right lighting make these birds sometimes appear green. It can best be described as a mottled or combination of small areas with different colors varying from yellow to grey.
This is a relatively rare mutation, and hardly seen outside of a breeders aviary or a show. There is a wide variation in the shades of the olive mutation, some being very pale and others quite a dark olive color. The olive cockatiels have a scalloped pattern in their feathers, with the outer edges of each feather being darker than the centers, making each feather seem outlined in a faint scalloped design.
Pastel Face is a less common mutation, and is much like how it sounds. The yellow and orange pigmentation in the cockatiels is diluted to a more �pastel’ hue. Making the face a pale yellow and the cheek spot a pale pastel orange. Note that it is different to the normal dull of the immature and female face, and is apparent even in the immature/female face as a clearly different, �pastel’, shade of yellow and orange.
Yellow Face/Yellow Cheek Yellow Cheek is one of the newer mutations and is unique in that there are Sex-Linked and Dominant versions of this mutation. Where a Normal Grey has an Orange cheek patch, the cheek patch of the Yellow Cheek is Yellow. The cheek patch of the Dominant Yellow Cheek seems to be a little more orange than the Sex-Linked version, but this can be more or less in individual lines of this mutation.
When breeding Yellow Cheeks it is important to never breed Dominant with Sex-Linked. It would take years of test breeding to determine what the offspring really are. It is also not recommended to breed Yellow Cheeks with Whiteface.
The Dominant Yellow Cheek is very similar to the Sex-Linked Yellow Cheek. Personal observations of the ones I have seen is that the Dominant Yellow Cheeks has a slight orange tinge, possibly due to a double factor, to it but lighter than the yellow-orange of a Pastel’s cheek patch. Single factor cheek patches are yellow.