Cuennei

Mother's milk can turn blue, but brilliant sky-blue if it has inordinate concentrations of whey protein. Normally this goes straight from the breast down the baby's throat, so it is a non-event and no one is any wiser for it. But women who pump out their milk might one day see a radioactive-looking fluid that seems fit for a spy novel, not a mammary gland.

Apparently this is all totally harmless.

This article here touches lightly on the subject of blue milk.

Disclaimer: do not take health or parenting advice wholesale from me, or from any blogger who does not provide a last name or list of credentials yadda yadda yadda.