Now let's talk about yellow-face budgies. Of course, all the normal green budgies have yellow faces. But some of the blue ones do, too. How does that happen? Doesn't the blue-gene tell the bird to stop making yellow coloring? So how does the face get to stay yellow in a yellow face?
There are several different types of yellow-face genes. They all sit at the same location on one chromosome, just like the greywing/clearwing/dilute genes did. The location where the yellow face genes live is the same location that the blue gene lives. Each yellow face gene does the same kind of thing that the blue gene does: they restrict the amount of yellow on the bird. The different types of genes you can get at that location are as follows:
Normals have rich golden yellow color on the face and the yellow color is all throughout the body, so that the feathers have yellow + blue = green.
Goldenfaced blues have a rich golden color to the face. The yellow color spreads throughout the body, but not as much yellow as you would find in a normal green.
Yellowface type 2 blues have a yellow face, less golden than the goldenfaces. The yellow color still extends over the body.
Yellowface type 1 blues have a yellow face, without yellow on the body.
Then there are the regular old white faced blues.
What about a pair of yellowface type 2 or goldenface genes? If you get two of those genes(it doesn't matter which two), the color is yellow or gold on the face plus a little on the breast, wings and tail. You get less spill-over onto the body than you would have with one yellowface gene and one regular blue gene. Again, it doesn't follow any logic that I can see, so it's just something to remember.
So, whenever you have a bird with a green gene at the yellowface site, and a grey gene at the blue/grey site, you get a grey bird with lots of yellow! We are in serious need of some examples at this point. Let's say we have a bird with the following genes: At the yellowface site, there is one Yellowface Type 2 gene and one regular (white face) blue gene. At the grey site, there is one gene for making the bird's dark pigment appear grey and one gene for making the dark pigment appear blue.
The grey gene wins over the blue one and therefore any blue coloration on the bird's feathers is turned to grey. So the outcome is a bird with a yellow face, a grey body, and yellow over it all. Sort of a grey-yellow appearance.
Momma has two grey genes at the grey/blue site. She gives one to her offspring. Momma has two whiteface blue genes at the yellowface site (remember, after the yellowface site gets done arguing for a white face blue bird, the grey genes step in and change the blue color to grey). So Baby gets a grey(not-blue) gene and a whiteface blue (no-yellow) gene from Momma.
Poppa has two blue genes at the grey/blue site; that is, they want the blue color to look blue not grey. At his yellowface site, he has two green genes; that is, he has the full amount of yellow. So, with his genes saying "Blue + Yellow," he looks green. Baby gets a blue(not-grey) gene and a green (fully yellow) gene from Poppa.
If the bird has one spangle and one normal gene, it looks spangled. If the bird has a pair of spangle genes, it looks almost like a dark-eyed clear, with just a few markings here and there. Not so much logic to it; just something to learn and remember. Let's do a little example to help remember about spangles:
I happen to think spangled budgies look pretty. Therefore, I want to breed them so that the babies have one spangled gene and one normal gene. How can I do it so that I get spangled babies and never get any with two spangle genes?
If I have one parent with a pair of spangle genes, and breed it to one with no spangle genes, every baby will get one spangle gene plus one normal gene. Therefore, all the babies will be visual spangles.
Ooooh, yes! More no-tech genetics!