I know this topic is over a month old, but I thought I would reply since nobody else had.
Genetics works like this:
2 parents can both have brown eyes; their offspring can have any eye color - brown, blue, green, hazel, etc.
2 parents with light colored eyes (blue, green) will only have offspring with light colored eyes. They cannot have a brown-eyed child. In your particular case, yes, it is possible for 2 people with green eyes to have a blue-eyed child, and vice versa.
On another note, if 1 parent has brown eyes and the other parent has light (blue, green) eyes, their children can have any eye color - light or dark.
Hope this helps....