Gray vs. Grey

Today has been quite a gray day in Pittsburgh.  Does anyone know the difference between "gray" and "grey"?  It's always boggled my mind...  I should probably figure it out since I live in one of the gray/grey-est cities in the U.S.

Lunch was a salad (grilled chicken and portobello mushroom) from a salad bar on campus and a yogurt.  I know some people have shifted away from these yogurts, because they contain high fructose corn syrup.  I'm all for organic/all-natural eating.  However, being a college-student, it isn't always easy to eat perfectly.  So, I figure, as long as I'm trying to eat as healthy as I can, a little high fructose corn syrup won't kill me.  Everything in moderation. 

And the 6th advent calender chocolate for dessert (I'm a bit behind...)

P.S. happy National Cotton Candy Day!