Pick the navy that is the darkest color on the same color chip card as the blue you already have. A red door in cranberry or ruby, but not if you have an iron security door in front of it. In that case, stick with black.

Replace iron railings with white picket railings as in the original photo. Add a tree to your front lawn and consider replacing the hedge with other bushes...specific tree and bushes depend on your planting zone.

I like the idea of black shutters and a red door!

Or no shutters, but beefed-up window trim: