It could possibly be the Fruit Loops, but I eat Fruit Loops pretty much every morning, and I have never had Blue/Green poop. In fact, I've never heard of Blue poop, until right now. I've heard of people having green stools. That's common if you eat alot of greens, like Spinach. Have you had any discolored poop since? or just that one time? Because if it's a continuing occurence, I would think it's something worse than fruit loops.
Here's an article I found about Stool Colors. It may shed some light onto your situation. Good Luck. Hope everything returns to normal soon.