What colour is this dress?

This dress has been raving on all sorts of social media today, posted//tweeted/shared by all your friends. They all ask a simple question: What colour is this dress?

Most people say it is either Blue/Black or White/Gold, and some may even claim that it changes depending on the time, weather, lighting, temperatures, handedness and so forth. Why is it so?

There are a lot of explanations offered on the internet now (Wired, Reddit 1, Reddit 2, Reddit 3), and I bet you can find the explanation that suits your taste the most. Yes, there is no conclusive answer to this so far, and my favourite answer is the colour constancy effect. It basically says that the colours we perceive depend on the context and illumination of the surrounding.

Look at these 3 photos under different white balances:

The middle is the original image. The left one has white balance on white, and the right one on blue. (Wired)

By changing the white balances, we can see the colours changed drastically. Our brain needs a reference point (white base) to tell other colours. The ambiguity in choosing the reference point makes our brain choose either side of the story, or in our case, of the dress.

There is an excellent illustration on Reddit that shows how different illumination may change the colour:

It can be either a black or white dress depending on the light!

A relevant optical illusion, also a favourite of mine, is this:

Checker shadow illusion. Or in today term, 50 shades of gray illusion.

What are the colours of tile A and B? Are they the same shade of gray? You can find out the answer yourself 🙂

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