I'll try to shed some light on the genetics. The green color is what I see from a 3rd or 4th generation cross where I am certain the hen is homozygous for the genes that turn on the porphyrin biopath. This is most likely a hen that is also homozygous for blue egg (oocyanin on chromosome 1). And last but not least, this hen likely carries 1 copy of the zinc white gene which gives the unique green cast to the egg color.
Presuming you want to breed pure pure sky blue eggs, you need homozygous blue egg, homozygous zinc white, and homozygous for the gene or genes that disable the porphyrin biopath. I've tried to characterize the genetics that turn off porphyrin in my birds and concluded that it is at least 2 different genes. Keep in mind that porphyrin is a complete biopath - a group of genes that work in concert to produce an effect. Porphyrin requires unique cells in the epithelium of the egg ducts. The more cells that produce porphyrin the darker the egg. The critical piece of information not published in a peer reviewed paper is that all extant chickens have the porphyrin biopath, but some of them have genes that disable it. This means that any cross with a chicken that has the genes for porphyrin production will always behave as a dominant gene. It will be expressed 100% in the progeny.
Also important, trace amounts of porphyrin can be detected by using a damp towel to wipe off an egg, then place it beside a sky blue egg. You can easily see the difference side by side when the egg is damp. Why is this important? It gives a simple test to find hens that lay pure blue eggs. Test mate to a rooster and the offspring egg color will tell you if the rooster has genes that turn on porphyrin. This is what your eggs are showing. A blue egg laying hen crossed with a rooster that has porphyrin enabled, result is chicks that lay green eggs.
Presuming you want to breed pure pure sky blue eggs, you need homozygous blue egg, homozygous zinc white, and homozygous for the gene or genes that disable the porphyrin biopath. I've tried to characterize the genetics that turn off porphyrin in my birds and concluded that it is at least 2 different genes. Keep in mind that porphyrin is a complete biopath - a group of genes that work in concert to produce an effect. Porphyrin requires unique cells in the epithelium of the egg ducts. The more cells that produce porphyrin the darker the egg. The critical piece of information not published in a peer reviewed paper is that all extant chickens have the porphyrin biopath, but some of them have genes that disable it. This means that any cross with a chicken that has the genes for porphyrin production will always behave as a dominant gene. It will be expressed 100% in the progeny.
Also important, trace amounts of porphyrin can be detected by using a damp towel to wipe off an egg, then place it beside a sky blue egg. You can easily see the difference side by side when the egg is damp. Why is this important? It gives a simple test to find hens that lay pure blue eggs. Test mate to a rooster and the offspring egg color will tell you if the rooster has genes that turn on porphyrin. This is what your eggs are showing. A blue egg laying hen crossed with a rooster that has porphyrin enabled, result is chicks that lay green eggs.
