From the pictures it looks like a solid darker colour used as banding on the bottom of the drapes would look fine, but since I'm not sure how they look in person my instinct would be to start from scratch I'd recommend getting new curtains, but be sure they're long enough to be hung several inches above the window frame. I'd also recommend that the curtains be made wider to give a fuller look to the window. What I mean is that the curtain rod and curtains should extend about 6-8 inches on either side of the window trim (more or less depending on the room), and that the curtains themselves should be made wider so that when they are closed the curtains fully cover the window and still retain some pleats. Alternatively, if you don't plan on opening and closing the curtains often, then just make them wide enough so they look full when drawn back. Making these changes won't be super cheap but I think the investment will be worth the return in this case!