Follow the light grey spot around the circle for 30 seconds to 1 minute, and you will notice the other spot will eventually turn green.
If you stare at the cross in the middle for 30 seconds to 1 minute, the spots around the circle will disappear.
I took the time to do this, and it works! The dots turned teal green, but had varying intensities. In the second illusion, most of the dots disappeared for a bit, but never did they all disappear. I just can't hold my eyes still enough. This illusion is an example of Troxler's fading. There's another, similar illusion at the Wikipedia link. I haven't yet figured out why there is a white dot in this illusion. Read more about this effect and see three other illusions at Lensflare. -via Boing Boing