Not sure where people are getting the idea to hang curtains outside of the window, these days. Curtains should be on a window, covering at least a few inches of the glass, or they'll look like fabric wall hangings rather than curtains. Doesn't look nice either.

Anyway, they should also be full enough to look like they'll close, even if always left open, so for a window that wide, you'll need a few widths (or a few panels if readymade) per side, which will take up a good part of your wall space also. Just hanging one panel there will look skimpy and ugly.

If you want them for decoration only, then pick a color from the rug. Matching to the walls make no sense.

If you're not going to ever close them, maybe just leave them off, as the window looks nice on it's own.