You already know that you like dark green, so go with it.

Black is classic but you should remove the shutters. Shutters should only go on windows where, if the shutters were actually closed, the windows would be covered, which eliminates your wider, triple window. The smaller windows above would be suitable for shutters.

What color is the roof and any other large part of the overall color scheme? Is the gutter downpour near the window brown? Take into consideration the patina of the copper detail above it as well as your door. Finally, what are your favorite colors in your wardrobe? That will tell you what appeals to you most.

Link those colors into your shutters to make a cohesive appearance.

Being you're leaning toward green, what about the darkest patina you find in the flashing?

I personally like blue over green, but whatever works really

The dark green would match perfectly with the plants along the base of your home.