Personally I love optical illusions, because they are good reminders that what we believe may be the truth is not always the case - it's all based on our biases (biological, psychological, emotional etc).
From the article I linked earlier:
So here are the two colours from the dress shown on there own - what do those who saw white/gold see now? What happens if you go and look at the dress on the first page?
From the article I linked earlier:
Both squares are grey, but you see one as yellow and one as blue. It happens because in both cases you unconsciously correct for what colour you think the source of light is.
We do that all the time to get by in the world: the reason you see a piece of white paper as white regardless of whether you're outside (under the blue sky) or inside (under red-tinted candle light) is because you shift the colour of the paper in your mind back to white – you white balance it. Or in technical terms, you "discount" for the "colour of the illuminant".
In the illusion above, on the left you correct for a light source you think is yellow, making the grey square appear blue. And on the right you do the opposite.
So now to that dress. The key thing is that we are correcting for an imagined light source, just as in the example above. But there are two features of this picture that make it very difficult to interpret, which means people are likely to see it differently.
So here are the two colours from the dress shown on there own - what do those who saw white/gold see now? What happens if you go and look at the dress on the first page?