What breed of chicken lays green eggs and how is the egg formed inside a chicken?

The Araucana and the Americana chicken are two breeds that lay green eggs.

The breed of a chicken determines what colour the eggs are going to be, it is a result of genetics. In a way, much the same as what determines the different colours that peoples' eyes or hair or even skin can be.

The egg of a chicken is formed in the hen by a reproductive system composed of an ovary and oviduct. Most females have two functional ovaries, but chickens and many other birds have only one ovary and one oviduct. In this oviduct, all parts of the egg, except the actual yolk, are formed. The yolk of an egg is formed in the follicular sac by continuous layers of yolk material being deposited. All of the yolk material is formed days before the laying of the egg. When the yolk matures, the follicular sac ruptures along a line with few, if any, blood vessels. If any blood vessels cross the stigma, a small drop of blood may be deposited on the yolk as it is released from the follicle. This causes most of the blood spots found in eggs. After the yolk is released from the follicle, it is kept intact by the viteline membrane, which is one of two membranes surrounding it. The release of the yolk from the ovary is called ovulation.

After being released from the follicle, the yolk enters the hen's abdominal cavity. The infundibulum of the oviduct surrounds the yolk with its thin, funnel-like lips. The yolk then enters the magnum section of the oviduct where the dense portion of the albumen (egg white) is added. The magnum of the oviduct is divided from the isthmus by a narrow, translucent ring. The isthmus is smaller in diameter than the magnum. It is here that the two shell membranes fully form. The shell membranes contain the yolk and albumen until the rest of the albumen is added in the uterus. The shell is also added in the uterus or shell gland portion of the oviduct. The shell is composed mainly of calcium carbonate, which is white. It takes about 20 hours for the eggshell to form. If the hen lays brown eggs, the pigments of the brown egg are added to the shell in the last hours of shell formation. Brown eggs get their colour from a substance called protoporphyrin , which comes from the breakdown of hemoglobin in the blood. This pigment is deposited on the surface of an otherwise white egg as the egg is formed and it can be rubbed off with sandpaper or dissolved off with vinegar. Blue and green coloured eggs come from a pigment called oocyanin that is produced in certain breeds of birds along with bile and is deposited a bit further down the oviduct. There are other pigments that can appear as egg colour, These pigments can turn eggs brown-red (oorhodeine), brick red (lichenoxanthine), or various other shades of blue, green and even lilac. Adding to the various shades, in the last portion of the oviduct, a thin, protein coating called "bloom" is applied to the shell to keep harmful bacteria or dust from entering the porous egg shell, this can produce a rose hue on an otherwise brown egg.