I know how genetics work, and I know what colors I will get when I pair mutations, but explaining it so that others can understand is an entirely different matter. I'm just not good at explaining it! Here I will give you the BASICS and nothing more. At the bottom of this page there is an excellent link that will offer you MUCH more insight and better explanations than I can give you!
KRISTEN REEVES, MEADOWLARK FARMS AVIAN SUPPLY, INC.
Black Head - in cock and hen birds, a pure velvety black that covers it's entire face and throat. A black headed bird carrying a double factor yellow head gene will have a yellow tipped beak instead of the normal red one.
Red Head - in cock birds, typically a deep shade of crimson red though it may range from crimson to "stop sign red", or even by throat of black. In hen birds, this red head can be anything from a pure red to nearly all black with a few spots of red in the is a red head until after her first adult molt, perhaps longer!
Yellow Head - 'Oy, orange, yellow - depending on who you talk to you'll get both yellow and orange but meaning the same thing. However, anyone who actually knows what they are talking about when discussing genetics will call this a YELLOW HEAD. Because there is no such thing as an "orange" gene, the true technical term is "yellow head" and should be named as such. A yellow headed bird has an almost orangish-yellow head, usually more orange than yellow, but never a true "yellow". Its beak tip will be yellow, not red. As with the red head cock birds, yellow head cocks the yellow is outlined by a deep velvety black. In hens, there may be mottling in the mask, and often times the black surrounding the mask also extends around the beak.
Purple Breast - in cock birds a deep royal purple. Hens have a rose or pale purple breast.
White Breast - a mutation occurring in both cocks and hens. If the bird is truly a "white breast", the white will be a pure white. Birds with flecks of any shade of purple in their white breast are considered "bad white breasted" birds.
Lilac or Lavender Breast - a mutation occurring in both cocks and hens. This color can range from a very pale purple breast, not unlike that in a normal hen bird, to a deeper purple not quite as deep as a normal cock bird.
First - The Easy Stuff
There are several color mutations currently known in Lady Gouldian finches. They are defined in "head color", "breast color" and "back color" and in most cases, may be a combination of any of these - the combinations are what makes explaining the genetics for these birds so difficult!
There are really only 3 back colors; Green, Yellow, and Blue. The genetic makeup determines whether a bird is "single factor" or "double factor". This will be explained in depth a little later!
Green or Normal - this green is a deep grass green. It is the same in cock and hen birds though cocks tend to be a bit glossier and the green may be a bit deeper. As with many other species of finch, the cocks are "brighter" and much more flashy than the hens.
Dilute Green - this is a paler version of the green back. The deep grass green and other colors on the bird are a bit washed out. Grass green turns to a lime green color. Black in these birds will be non-existent. Even in a black headed bird, the head can appear more gray than black. Hens cannot be dilute. Dilute chicks in the nest will be much paler green than their normal colored nest mates.
Yellow - this yellow may be light - like lemonade - or deep in a color I like to call garlic butter. It is the same in cocks and hens and may even contain a greenish tint. Occasionally, single factor yellow birds will have single or several spots of pale green in their back feathers. Many breeders will attempt to breed this green spotting out of their yellow birds as it is considered a "fault". Yellow chicks in the nest will have what appear to be "red eyes" for the first few days after hatching, and will be very pale in comparison to their nest mates.
Blue - blue backed birds are almost a dusty grayish blue. Again, the depth of blue and the actual color of the blue with depend on the genetics of the parent birds. Blue chicks are steel grey and will look obviously different from their green or yellow nest mates.
Pastel - pastel birds are the "dilute" version of a blue backed male. Here again, hens cannot be "pastel"
Silver - silver birds are nearly white and are part of the "blue" mutation. Consider it the "yellow" of the blue line. LIke dilute greens, they come in both single & double factor.
It may help to think about the colors like this:
The "greens" - these birds all belong to a less complicated genetic pool starting with the basic normal green. The ability to process "lutein" or yellow, and "melanin" or black, plays a large factor in their color once you stray from the normal to dilute or yellow - Normal Green, Dilute Green, Yellow.
The "blues" - these birds belong to a more complicated genetic pool. The inability to process "lutein" or the LACK of yellow plays the largest factor in their coloring beginning with the blue, then moving on to the inability to process "melanin" in the pastels and silvers - Blue, Pastel, Silver.