Line a baking sheet with parchment paper, ensuring it covers the entire surface to prevent sticking.
In a microwave-safe bowl, add the 12 oz. of bright white candy melts. Microwave in 30-second increments, stirring between each until fully melted and smooth. Avoid overheating.
Pour the melted white chocolate onto the prepared baking sheet. Spread into an even layer about ¼ inch thick using a spatula.
Melt the dark green and red candy melts using the same microwave method. Drizzle over the white chocolate layer in a random pattern. Swirl colors together slightly with a toothpick or skewer for a marbled effect.
Before the chocolate sets, generously sprinkle holiday sprinkles over the top for a festive crunch.
Allow the bark to set at room temperature for 1-2 hours, or refrigerate for about 30 minutes to speed up setting.
Once set, lift the bark off the parchment paper and break into pieces using your hands or a sharp knife.