Chromostereopsis

The effect varies for different people. Take a moment and look at this. Some people don’t see anything special: just a blue iris in a red eye. For me though, there is an incredibly strong depth illusion – the blue and the red appear as if they are at different distances. I can enhance the effect by blinking rapidly, turning the brightness up on my screen and viewing in a dark room. Sometimes it disappears for a few seconds before snapping back in. Because the colours appear at different depths..