Spoiler alert
the dress really is Black and Blue, however the reason why it looks White and Gold is because whoever took the picture over exposed the photo and caused it to become white and gold. the reason why one person can perceive it as blue and gold and another white and gold is because some peoples brains under expose what they see, compensating for the over exposure, while others peoples brains will just except what is being seen.
...at least thats what i read.