Stare at the white dot in the centre of the red circle. The longer, the better (two minutes and you’ll get a much stronger effect). Always try to keep focused on the white dot. It’ll be worth it.
Soon after starting, you’ll start to see a thin rim of light around the edge. Don’t stop staring yet! Wait another minute – keeping your head perfectly still.
Once you’ve done this, very slowly – move your head backwards – making sure to keep your eyes focused on the dot at all times.
Voila, "true cyan." Note that this color doesn't match any of the shades of blue in the palette on right, thus this color can't be displayed by your monitor.
Nothing in the real world has this color; it can only be perceived as an illusion caused by saturation of cones in the retina.