Here's a neat demonstration of this https://www.schulz-hildebrandt.com/9-purple-dots-illusion/ https://www.schulz-hildebrandt.com/9-purple-dots-illusion/ (I fi

Here's a neat demonstration of this https://www.schulz-hildebrandt.com/9-purple-dots-illusion/ https://www.schulz-hildebrandt.com/9-purple-dots-illusion/ (I find the effect works much better on my phone screen than desktop)