Stare directly into the dot at the center of the circle, firstly you'll notice that the area where the circle is missing will turn into a green circle (what!?) and eventually, you'll only be able to see that single circle.

What: The Lilac Chaser is perhaps my favorite illusion of all time, largely because it combines so many different illusions into one amazing piece. It was first built by Jeremy Hinton in 2005, and has made the internet rounds many times! To get this thing going all you really need to do is focus on the dot in the center, the rest should hit you one effect after another.

The first effect I observe is the afterimage effect, whereby the empty hole in the circle suddenly gives you a circle of the inverted color, so at its initial settings, there will be a green circle… that alone is amazing.

After that, you’ll get hit by the Troxler Fade, whereby the gradient circles should suddenly disappear. Often for me, it is as though the green circle eats them up and they’re gone.

After that, of all things, the green circle will keep circling… if you stare that this for a really long time, and then look away you’ll still be seeing green, it’s incredible.

How To: Here you can mix up the colors, and the amount of dots, you’ll be able to see that the inverse disc can more or less show you the full gamut of colors.

Cites and Extras:

I've researched these optical illusions in my spare time but am clearly not any kind of expert and my explainations are pretty smooth brained, if you find something mis-cited, earlier examples, or general mistakes please new let me know via, be kind!