The reason why we’re all so split over the colour of the dress? Because of how the eye sees colour. As Bevil Conway, a neuroscientist who studies colour and vision at Wellesley College explained to Wired:
What’s happening here is your visual system is looking at this thing, and you’re trying to discount the chromatic bias of the daylight axis. So people either discount the blue side, in which case they end up seeing white and gold, or discount the gold side, in which case they end up with blue and black.
As one blogger puts it, "a dress hasn't been talked about this much since Monica Lewinsky".