viral – and the reason why is quite baffling. At first glance, the snap shows the pals posing together as one of them is holding a tortoise.
But what you don't realise is that the image is actually an optical illusion which means it's technically in black and white.
Digital artist Stuart Humphryes shared it on Twitter explaining how it demonstrates the "colour assimilation grid illusion".The London-based content creator simply added a grid featuring colourful lines over the black and white image.He explained how our brains "fill the gap" of colour perception and apply the grid colour to the rest of the picture.
In the shot, the teenagers T-shirts look green, blue, yellow or red, and the tree behind is green. But on closer inspection, you.
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