Does happen, was repetedly discussed (for instance in [thread=5007]January[/thread], [thread=6909]February[/thread] and [thread=17309]May[/thread]), but it still appears as if no one has been able to pin down the ultimate reason for the color change, besides some general remarks in the line of possible oxididation or influence of sunlight and temperature. If your juice is still clear, anything living in it is highly unlikely. Though green is not necesarily problematic, JC will replace. Keep us posted if you get a verdict upon the causes for color change.