I think it's a good idea. Dark railings, etc, allow one to see past them far more easily than light ones do. So unless you specifically want the view to be framed by your windows, avoid light colours. My front garden security fencing is dark brown for precisely that reason -- so we can see any suspicious activity outside. You have to live here to understand that. (And yes, black is a bit harsh.)

I had to stop biting my lip with jealousy for your tree-top view before writing this.

Thank you for your opinion Rina. I don't want to make a costly mistake that I'll have to live with for the next 20 + years. And we're blessed - it's a lovely view - which is precisely what I don't want to detract from.

Absolutely. Just be careful to choose carefully among any browns that are available. Hold them up against the window, and see how they work with the interior. But in the darker shades browns are more forgiving of matching than in their mid tones.