Go on full screen, click the green flag and fix with your eyes the white cross. After some time (normally 40 seconds), the backdrop will turn black and for a few seconds, you will have the impression the see a blue that is darker than black (sometimes not at the start when the backdrop just changed but when the blue circle is fading). That blue is Stygian Blue. If your screen is bright, you might want to change the input of the "wait block" from 40 to 20 seconds.
Stygian Blue can only be seen by fatiging your M and L cones in your eye.
