is blue and black (http://www.independent.co.uk/life-style/fashion/news/the-dress-actual-colour-brand-and-price-details-revealed-10074686.html).

The lighting in the photo causes some people's eyes to discount the blue shades of the dress and see white.

Even still, the actual dress itself is BLUE & BLACK. Period. The color of the physical dress isn't up for debate. The picture is what's open to interpretation.

"All the world's a stage,
And all the men and women merely players:
They have their exits and their entrances;
And one man in his time plays many parts..." -The Bard