I posted this little optical illusion yesterday on BlueSky and it proved so popular I thought I’d repeat it here.Whichever of the purple dots you look directly at turns more purple:
I find the effect is stronger on a smaller screen (e.g. on a phone).
In a nutshell, this happens because your eyes have reduced sensitivity to blue light at the centre of your field of view so the purple (which is a mixture of red and blue) changes hue if you look directly at it. For more details see here and the following blog post:
I’m interested to know whether or not this works for people who are colour blind, so if that is you please let me know!
In the Dark 