Quote:
There may be 12 genes that cause brown egg color- brown eggs are genetically white also, so brown eggs are o+/o+. Brown egg pigments are normally added to the outside of the shell.
Chickens that produce white eggs do not have any brown egg genes and are o+/o+, some have recessive sex linked genes ( only one paper on this and I am too lazy to go find it) that work to eliminate color in egg shell. No pigments are added to the shell or the outside of the shell. Found in white leghorn.
Blue eggs are produced by birds that carry O/O or O/o+. The O gene is a dominant gene that adds blue pigment to the shell.
Green eggs are produced by a bird that has a blue egg shell gene or genes and brown egg shell genes. Darker green has more brown pigment added to the out side and light green has a little brown pigment added to the shell.