Do you see blue or purple? Optical illusion divides the internet

"On social media, commenters were bitterly divided over whether the dots were blue or purple. However, some commenters pointed out an even stranger effect. One viewer wrote: 'Only one is purple to me, but it keeps moving around.' 'My perception of the color changes depending on whether I'm focusing directly on the dot,' another added. And another joked: 'How does the purple dot know to change to where my eyes are looking?'"

"Although this might seem strange, this is exactly how the illusion's inventor, Dr Hinnerk Schulz-Hildebrandt, intended it to function. In reality, all of the dots are a bold purple and placed on a blueish background. But, by holding your phone about 30 cm from your face and looking at each dot in turn, only the dot at the centre of your current focus should appear to be purple."

"In another variation, 360 purple dots are placed on the same blueish background. By holding your phone about 10cm from your face and slowly moving it further away, you should see more and more dots changing from blue to purple as your area of focus expands. In a final version, Dr Schulz-Hildenbrandt created a 'vanishing poem' using text in the same purple and blue combination. Holding your phone close to your face and reading carefully,"

A color-based visual illusion uses nine bold purple dots placed on a blueish dark purple background to create shifting perceptions of color. Observers report that some dots appear blue while others appear purple, and that the perceived purple dot moves depending on gaze. The effect arises from the interaction of identical dot color and surrounding background color combined with focal attention. Viewing instructions change perception: holding a phone roughly 30 cm from the face and looking at each dot in turn makes only the dot at the center of focus appear purple. Variations with hundreds of dots or vanishing-text versions expand the same attention-dependent perceptual change.

Read at Mail Online