Stare are the circle (below) for about ten seconds and your brain will eventually perceive it as red! Try it, you’ll see!

Reddit user SEILogistics has the explanation:

It’s caused by a prefrontal imbalance of the auxiliary nerve on the eye retina created by the spheroid object being stared it. It confuses the obsidian prenatal synapses in the brain.

If you’ll notice on your peripheral vision you can see the prenatal synapse snapping on the right of your field of view before it turns red.

As your prefrontal cortex adjust you can see the neuropathic synapse being repaired in your eye and the circle centre returns to its normal colour.

[Source: Crinchy on Reddit]