optical illusion clip used to explain how colour blindness works has left viewers in awe.The BBC Archive shared a 1985 video of an unusual Union Flag in the colours of yellow, black and green.At the beginning of the clip, the presenter asks viewers to stare at a black dot in the centre of the flag until it disappears.The screen then subsequently appears being blank, and most people will see the Union Flag in its traditional red, blue and white colours.The presenter reveals that the illusion can be explained by the simple "three receptor theory" – which is based on the colour-sensitive cones in the retina of the human eye, corresponding roughly to red, green, and blue sensitive detectors.As you stare at the green area of the image, your.
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