The dress is shown with the shadow side facing towards the camera, and coupled with overexposure this explains the blue-ish tint of the dress. The same phenomenon happens in stronger degrees when when you look at snowy mountains for example.
With that said, the way to more accurately determine if the color is blue and black, is to look at the values. More specifically, the other fabric in the left bottom corner. The value of the black fabric in the corner is darker, even when lit, than the darkest dark of the gold value, meaning the dress has no black in it. It just doesn't add up for it to be black and blue.
Studying how value, light, color and shadow is perceived for painting purposes for 6+ years, I can guarantee with a great degree of certainty (despite the piss poor quality photo) that this dress is not black and blue, but that its local colors are gold and white. Obviously because of the environment and shadows, this shows up as blue and brown in the photo. And the shitty exposure changes in the OP do not prove a thing.
A simple explanation could just be that this dress is one of the many variations, as the Roman website shows this dress isn't exclusively blue and black, it also has white and black, red and black etc. And not to mention that this could just be a bootleg product.