1. Place half-slabs of any kind on the ground and two blocks above a normal block to make it only passable while crouching
2. Enter it while crouching
3. Let go of the crouch button
4. Walk backwards out of the 1.5 height space
5. Observe screen flash

While using a 1.13.2 resource pack this effect only occured the other way around. That means I had to leave it while walking forwards to make the screen flash.