Line a large baking sheet with parchment paper and set aside.
Add white chocolate to a large microwave proof bowl and heat for 45 seconds. Stir then continue heating for 15 seconds, stirring in between, until melted and smooth.
Working quickly, pour melted white chocolate on the lined baking sheet and spread out into a large rectangle.
Melt the candy melts in the microwave in small separate bowls until smooth.
Drizzle the colored candy melts onto the white chocolate and use a toothpick to swirl.
Sprinkle on the Lucky Charms marshmallows and rainbow sprinkles all over.
Place the baking sheet with the bark in the fridge to harden and set.
Remove from fridge and use your hands to break into chunky pieces.