Your green stools post is the most informative of any websites, etc. Where did you learn about green stools?
Are you sure that the Korean Seaweed is safe? Sounds to me like that's what is reeking havoc with your system. You have to be very careful with things like this, as there is no regulation for them. Nobody is watching to make sure it is safe for human consumption or what side effects they have. But I agree that these 2 things are what is coloring your stools green.
Changes in your diet can cause changes in fecal color, colonic transit time, and gas. Give your body some time to get used to the new diet. Green isn't really a color to worry about when it comes to this sort of stuff.