I promise the circle doesn't change colour (Image credit: Lenstore)
According to the Lenstore(opens in new tab), the reason we think the colour of the circle changes is because "Cells send information to our brain through the optic nerve and the brain from that signal tries to interpret what we see. When judging colour, the brain perceives it differently when it is compared to what is surrounding that object, suggesting why we think the blue circle changes colour in this illusion".
Still don't believe it? Well, Lenstore also shared proof of the circles all being the same colour (see below). This isn't the first colour-related optical illusion they've produced that has left us feeling confused. Back in August, we saw a hypnotic orange optical illusion that left us feeling just as baffled as this one.