Why? It's not that clear cut, because the brain can do some colour-temperature processing and correction of its own. In the case of this bad photo, the cues for doing that are ambiguous, so some people's processing enables them to reach the blue and black of the dress, while other people's leaves them with the white (with a hint of blue) and gold that are actually the colours in the photo.
The only mystery in my mind is why Metope continued to see the corrected photo wrong. It seems to me that the background picture on the wall, for instance, although a touch muddy, has essentially natural colours, so there's no reason for the brain's colour processing to go into overdrive to force the wrong colours out of the perception of the dress. But clearly her brain disagreed, as when I removed the background, that processing stopped.