Embarrassing, but what could cause blue green feces? I do not feel sick at all. Could a sudden intake of more iron and zinc cause this?

Blue/green stool. Blue food coloring is a popular food additive, and when ingested in large quantities can make stools appear blue. Blue is not a pigment typically produced by the human GI tract. Blue is however the color of ingestable "indicator" dyes & that a hemoccult card will turn if blood is detected in stool (or it taking a lot of iron, as in your case)--is this to what you are referring?