First of all... that dress looks stunning on you, and I think the color of it is far prettier than in the stock photo. I would like to venture the opinion/idea that you should have someone do your makeup and hair, and take another photo in your dress, in similar lighting to what you will have at your wedding and reception.
I think there has been some wonderful feedback for both sides. For my part, I fall somewhere in the middle. Wedding dresses are too expensive not to have one that makes you feel absolutely divine. But it is also a dress that you will wear once. I have watched many friends and family set impossibly high bars for life events - wedding, prom, Valentine's Day - and what is supposed to be a beautiful, happy gathering of loved ones, turns into tears and dissatisfaction if every little thing doesn't go absolutely perfect. They looked absolutely divine, their event was breathtaking... and there was a layer of unhappiness putting a light layer of tarnish over everything.
It is up to you to decide: is this dress something that will haunt you and ruin your day? If so, I would contact that designer again, and point out firmly, that you want to return the dress. If she is unwilling to make this right, you will post side-by-side pictures on every bridal site you can find, and leave an honest review of her business practices. Be calm and cool in your wording, and succinct - and hopefully that helps change her mind. I agree with you that this does not look like the same color and fabric as the photo, even allowing for photoshop and/or lighting. The beadwork is different for sure. The dress you are wearing has far more beadwork on the shoulders than the dress on the model.
In truth, if you wind up stuck with this dress, you should be able to resell it as a pageant gown. It is truly a lovely dress.