A remarkable test shows the participant how their brain responds to colour.

Designed to make us to think about the work our brains put in so we can process the light that streams into our eyes, it features in the new BBC Four series, Colour: The Spectrum of Science.

The video below shows a black and white photo of a castle.

Once you click "play", the image should turn into a colour negative with a bright blue dot in the middle.

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Keep your eyes focused on the blue dot. Don’t look away. What happens next?

The black and white image should suddenly appear in full colour. The optical illusion will wear off, but this is your brain essentially colouring in a black and white image.

You can see the same effect in this video from Cardiff University.

Dr Helen Czerski said she wanted to explore the 15 colours that tell the story of Earth, life and scientific discovery in the new BBC Four series.

"The world is ablaze with colour," she said.

"In the otherwise dowdy solar system, Earth stands out from the blackness of space as a multi-coloured jewel. But how did a drab grey rock become filled with colour?"

From the largest solar telescope in the world in California, to the mountains of Tennessee, she will look at what colour is, what it does, and why it does not exist outside of our perception.