Yeah- it's probably the antihistamine or traces of it if it was not removed entirely. I've seen the same kind of gear floating around, and it turns either aqua marine or emerald green, as you describe.
Some of this gear has been outstanding, so I vote harmless on the trace amt. of Triprolidine or Chlorpheneramine. Remember that very small concentrations of impurities can cause visible color changes in the outcome of organic chem experiments, so it's possible this stuff has been removed in large part and the overall chemistry may not be sloppy- but you know, it's also a sign that someone took a shortcut or didn't do one of the steps entirely properly.
Another theory is that it's trace amounts of the green dye used to color pretty the large horse-pill styll 120mg + 240mg slow-release gel-caps. But i've never seen stuff turn purple or some of the other colors used in the gelcaps...