Not sure you can pick a shade accent color based on something that may or may not be moved around frequently (the vase)

What other colors are in there? Sofa? Chair?

The sconces are gold, dark hardwood floors.

Then I'll vote gray, but Revere Pewter is rather warm, so be sure that the trim is warm too. If it's just too iffy to guess, then go with the blue.

Whichever color you choose, be sure to mount it in the "blind light" the blank area above the window, just below the crown molding. Then, in the daytime, you can lower it enough to cover just the top of the window, both to reveal your pretty color/pattern, and avoid depriving yourself of daylight, and it will make the window look taller and the room higher both by day and by night when they are lowered all the way. It's an old trick used throughout Britain and the Continent, but little known in America, which is why American windows so often look short and squat. Good luck with the color choice.

A roman isn't meant to be mounted like that, just sitting on top of a window. Would look stupid, IMO. There isn't enough room on top of your window to make a difference anyway. It would have to be a very short roman in order to clear the glass and then you couldn't pull it all the way down. I like inside mount better.

There's so much going on around the window, if you must have banding, I think gray to blend in more.

I'd remove the pictures from the table and just leave the vase. With two matching sconces and two matching pics (or the frames at least), it's too matchy, I think. If you want to display the pics, perhaps stack them on a wall nearby.