I've always imagined the dress to have a medieval sort of feel to it, mostly because I see nearly everything in Narnia as having medieval style. It's got to be a dress that parts well to the sides, because it's a riding dress, after all. Of course, she was probably riding side-saddle; but she still would have to have had a pliable skirt. As for the shade of green, I imagine it to be something that shimmers, like the scales of a serpent. Of course, the underfabric of the split would most likely not be the shimmering material. That part would have to be of a softer texture, and it would most likely be a lighter shade as well. Then again, the darker shade could be underneath while the lighter shade is on top... that would create an interesting contrast, though unlikely for a riding dress because the emphasis would want to be placed on the overdress. Now, as for the accents... it could be either silver or gold, depending on the model's complexion. A silver chord would be tied around her waist, in keeping with the medieval theme. She would also most likely have her head adorned with some sort of circlet... and I have always imagined her as having red hair. Why? Because the image of a person in a green dress practically screams red hair to me. Okay, so that's how I imagine it and whatnot. It'll be interesting to see how your dress actually turns out.