Studies seem to indicate that the pigment isn\'t synthesized in the bloodstream as originally thought; it is actually synthesized in the egg shell pouch:
A Study on Eggshell Pigmentation: Biliverdin in Blue-Shelled ChickensHowever, this specific study was performed on a variety of Chinese blue-egg laying chickens (Dongxiang fowl). The genetic background is claimed to be similar. I don\'t think this would change anything as regards trying to feed some additional zinc for color, though, as the color still comes from the same element, whether synthesized by a breakdown of blood cells, or synthesized in the egg shell pouch.
However, it may be more worthwhile to simply select breeding stock for darker eggs if that\'s what you\'re interested in. I\'ve seen a lot of variation, with some \"bluer\" eggs even toward the end of the season when eggs (in general) are lighter in color. Sometimes slower layers will lay these... and sometimes not. Sometimes one hen just seems to lay darker eggs.
I seem to recall a very good site selling Ameraucana chicks and even offering individual breakdowns of how docile each color was, how well they laid, how blue their eggs were, etc. I think this was chickhatchery.com? Yes... the information is on this page:
FAQsYou will want to scroll down for the nice chart. For me, docile, friendly birds are the most important. I have wheatens and they are wonderful. I see buffs are listed as even more docile than the wheatens in this stock, so I am intrigued...
Looks like some of the bantam stock may lay some of the darkest eggs there.