Line a large baking sheet or tray with parchment paper or aluminum foil.
Place 12 ounces white chocolate chips in a large microwave-safe bowl. Microwave in 20-second intervals, stirring after each interval, until the chocolate is completely melted and smooth.
Place 6 ounces red candy melts in one microwave-safe bowl and 6 ounces blue candy melts in another. Microwave each bowl in 20-second intervals, stirring after each interval, until smooth.
Pour the melted white chocolate onto the prepared baking sheet and use an offset spatula or the back of a spoon to spread it into an even layer about 1/4-inch thick.
Drizzle the melted red and blue candy melts over the white chocolate, alternating colors across the surface.
Use a fork or toothpick to gently swirl the candy melts into the white chocolate. Avoid overmixing so the colors remain distinct.
Sprinkle 1/2 cup red, white, and blue M&M's and 1/2 cup red, white, and blue star sprinkles evenly over the bark. Gently press the toppings into the chocolate so they adhere.
Refrigerate for 30 to 60 minutes, or until the bark is completely firm.
Break the bark into approximately 24 pieces and serve.