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. Image: CC-BY Tom Stafford 2022 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 they even appear to glide separately when I move my head from side to side, something which is obviously impossible for a static image. The effect is called chromostereopsis and it is weirding me out, for several reasons. The first is that I’d thought I’d seen all the illusions, and this one is completely new to me. Like, guys, did you all know and weren’t telling? The second is that there are big individual differences in perception of the effect.…