If you find you find your ham has a green iridescent sheen to it, dont throw it away! It might still be good. Here are a couple of explanations why your ham may be green but still edible:
You are likely to find such a sheen on foods containing traces of fat
in water. When it is cool this mix separates out microscopically into a film, like oil on a wet road.
In some types of cold meats, such as sliced silverside of beef or some hams, you may see a handsome opalescence. The beauty of an opal results from light being refracted and diffracted by arrays of microscopic beads of glassy material in a matrix of a different refractive index. In the meat, the effect is caused by microscopic spheres of fat dispersed in watery muscle tissue. Heat up the meat and you destroy the droplets and change the optical character of the matrix so that the effect is spoiled.
The green colour that is sometimes observed on bacon
and ham is the result of the action of nonpathogenic bacteria which break down the oxygen
transport protein myoglobin
to produce porphyrin derivatives. These derivatives are large heterocyclic
compounds which can have greenish colours.
Source: The NewScientist - contributions by Stephanie Burton and John Richfield