Stool color can be greatly influenced by what you eat (food colorings/dyes); as well as an increased incidence of gastric motility. Bile is a nice little green/yellow color in general, so if GI motility is increased, the transit through your GI tract is much shorter in duration. This results in less time for enzymatic reactions to occur in which bile is further broken down. The end result of this normal breakdown process is what equates to the typical "brown" stool color we all know. If the process is incomplete due to a rapid transit process as described above; a more green colored (or streaked) stool can be present.
In all likelyhood, it's probably a combination of factors here based on what i've read about the ingredients. I'm sure the incidence in what people are seeing here is very benign in nature. I'll see how it affects me here in about a week.