When the player undergoes the Darkness effect pulsing as the Lightning flashes, the blocks can momentarily turn blue.

Steps:
1) Set up 2 observers facing each other connected to a sticky piston pushing a lightning rod up and down

2) Set weather to Thunder and throw a Trident with channelling on to the top of the lightning rod for constant Lightning bolts to be created

3) Give yourself the darkness effect (with pulsing set to 100% for more obvious results)

Note: Hiding Lightning Flashes in accessibility settings does not affect anything here